bash check if file is empty or whitespace

file.txt Remove completely blank lines (including lines with spaces). The regex version is more general, since it also finds \t and \n and \r. Join Stack Overflow to learn, share knowledge, and build your career. Are you saying that you want to know that: a) there is a single/double quote around a space b) a single/double quote along with a space c) something altogether different from that? To navigate to a directory with spaces … If the length of STRING is zero, variable ($var) is empty. This can be done using the -n or -z string comparison operators.. How to echo shell commands as they are executed. even simpler: no need to quote line, if you use bash's [[ syntax: @pihentagy Umm, that has the same number of characters, and the square brackets, re. Stack Overflow for Teams is a private, secure spot for you and I am not sure if you meant you want to skip lines that is empty or if you want to skip lines that also contain at least a white space. If you write myfiles="file1 file2", with spaces to separate the files, this can't work with file names containing spaces. Podcast 302: Programming in PowerPoint can teach you a few things. How to mkdir only if a directory does not already exist? Note: Your filename can be anything but for this article, we will be using “file name.txt” as an example.. C++20 behaviour breaking existing code with equality operator? Can you MST connect monitors using " 'displayPort' to 'mini displayPort' " cables only? Check if folder /data/ is empty or not using bash only features. Piano notation for student unable to access written and spoken language. How to pull back an email that has already been sent. By default, bash reads these files when it is invoked as a login shell (see INVOCATION below). @nhed: In the case of single characters, you can use a character pattern instead of the pipe character alternation. Passing blank line from file as argument to bash script. Please people, like @codeforester, keep it simple; the best software always is. Check if file exists and empty or not empty using double brackets [[..]] rev 2021.1.8.38287, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide. Please allow me to toss in 2 cents on Linux file names from a little different direction. All of the answers, including the top answer, seem like extra work. Should I "take out" a double, using a two card suit? Remove blank lines (not including lines with spaces). How do I set a variable to the output of a command in Bash? If the file is empty, then the job script should finish EOJ. This worked, the other ([ -z "$line" ] && continue) did not work. Please help Thanks. Create a Bash script which will accept a file as a command line argument and analyse it in certain ways. Create a Bash script which will take 2 numbers as command line arguments. Why does Steven Pinker say that “can’t” + “any” is just as much of a double-negative as “can’t” + “no” is in “I can’t get no/any satisfaction”? Effectively, this will return true for every case except where the string contains no characters. Plotting datapoints found in data given in a .txt file. Join Stack Overflow to learn, share knowledge, and build your career. While creating a bash script, it is commonly helpful to test if file exists before attempting to perform some action with it.. You can pass the -z option to the if command or conditional expression. Since read reads whitespace-delimited fields by default, a line containing only whitespace should result in the empty string being assigned to the variable, so you should be able to skip empty lines with just: [ -z "$line" ] && continue From what I understand, seta found a space only in 1117159 line of his file. Is there any solution using sh/sed/tr (in case bash is not installed)? I discovered that the spaces in the file names was a villain when using most backup programs at that time. [:space:] "Whitespace characters such as space, form-feed, newline,carriage return, horizontal tab, and vertical tab", note that this doesn't detect tabs or newlines, for those who are curious, I like the use of this syntax, but you've flipped the search and are seeking the opposite of what OP asked for. ; delete all horizontal space, including the horizontal tab character, "\t"delete all whitespace, including newline, "\n" and othersThe right tool for the job Is it normal to feel like I can't breathe while trying to ride at a challenging pace? How to check for whitespace characters using sed or grep in shell script? How to check if a string has spaces in Bash shell. for mentioning spaces some of the commands.. For example if we take “for loop” to convert all the files in a given directory we will face issue, because for loop will take space as a separator between given entries Navigating to a directory with spaces in the directory name. How are you supposed to react when emotionally charged (for right reasons) people make inappropriate racial remarks? Where is this place? Example – Using While Loop. Now I need to check if the line contains any non-whitespace character ([\n\t ]), and if not, skip it. I've tried the following things to match an "ok" surrounded by whitespace on either side, but Stack Exchange Network Stack Exchange network consists of 176 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to … Following example proves the same. How to get the source directory of a Bash script from within the script itself? In Europe, can I refuse to use Gsuite / Office365 at work? How to get the source directory of a Bash script from within the script itself? site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. Bash test for whitespace. I have tried using the "[[" syntax as well but to no avail. From the Linux and Unix bash(1) man page: nullglob If set, bash allows patterns which match no files to expand to a null string, rather than themselves. How can I check if a directory exists in a Bash shell script? eg. How to find out if a preprint has been already published. I was just working on a Linux shell script, and ran into the ages-old problem of handling data that has spaces (space characters) in it. if it does, then I want to add '"' double quotes at the beginning and end of the line. I often need to detect any white space, e.g. It will print to the screen the larger of the two numbers. Angular momentum of a purely rotating body about any axis. No. Here is a simple script to pass a file path to ls or chmod but filenames with spaces don't work even when enclosed in quote marks. grep "\S" file.txt Note: If you get unwanted colors, that means your grep is aliases to grep --color=auto (check by type grep). For example. Should mention, For those interested in this solution, my. How can I check if a directory exists in a Bash shell script? 2. How to check whether a string contains a substring in JavaScript? To check if string has ONLY spaces, tabs, or new lines, try: I'm nitpicking, but you don't need to quote $var. So, sed should remove since it is the only instance in that line. grep "\S" file.txt Note: If you get unwanted colors, that means your grep is aliases to grep --color=auto (check by type grep). grep . Here ‘cat‘ command will consider file and name as two arguments rather than a single argument. This page shows how to check if a file is empty in Bash shell running on a Linux or Unix-like operating systems. Slicing a bar in three pieces - probability. In some cases, you may be interested in checking if a file exists or not directly in your Bash shell. Usually your not only interested in detecting the space character. I have an output file from a previous step and I need to run "something" in the next step to check if the file is empty. The below script will check if the file exists and the file is empty or not. However, I am getting the same output for all the 3 mentioned strings. From what I understand, seta found a space only in 1117159 line of his file. Say a string might be like "a b '' c '' d". Create a Bash script which will take 2 numbers as command line arguments. Code: So, sed should remove since it is the only instance in that line. How can I test if line is empty in shell script? The following code substitute all characters between the squared brackets (space and quotes) with an underscore. disadadvantage here: If the part in the if is long, you get a code difficult to read. It will print to the screen the larger of the two numbers. To learn more, see our tips on writing great answers. How do I convert a String to an int in Java? However, any line which contains whitespace will not be considered empty. Otherwise leave the line as it is. Block-special files are similar to regular files, but are stored on block devices — special areas on the storage device that are written or read one block at a time.-c file Making statements based on opinion; back them up with references or personal experience. Why not approach it simply... To subscribe to this RSS feed, copy and paste this URL into your RSS reader. So you could run: if [[ -z "${DEPLOY_ENV}" ]]; then Bash Cheatsheet: check if environment variables are set or file/symlinks exists + more A bash scripting cheat sheet for developers who just want to get by. I think one of the most wanted examples is to check if a file exists and execute code according to the result. The PHP function empty is often used to check if a particular variable is empty or not (duh). cleanest one IMO, for me I also added tab but looks a little funky as I had to throw the dollar-quote in there. Stack Overflow for Teams is a private, secure spot for you and TAB. 2. Can this equation be solved with whole numbers? Check if File Exists and Not Empty. Quantum harmonic oscillator, zero-point energy, and the quantum number n. Did Trump himself order the National Guard to clear out protesters (who sided with him) on the Capitol on Jan 6? dotglob – If set, bash includes filenames beginning with a . file.txt Remove completely blank lines (including lines with spaces). Just to check if a string has any single quote and if it has any space. What are the key ideas behind a good bassline? Writing setup, CI and deployment flows means a bit of the old bash scripting. Bash Cheatsheet: check if environment variables are set or file/symlinks exists + more A bash scripting cheat sheet for developers who just want to get by. cat file name.txt Running the command without using escape character or quotations. I need smth that would work in both bash and sh. No. your coworkers to find and share information. you could check if the file is executable or writable. In Bash you quite often need to check to see if a variable has been set or has a value other than an empty string. -a file: Returns true if file exists. I am running a C shell script. #!/bin/bash if [ -a "/home" ] then echo "/home directory exists." The -s option to the test builtin check to see if FILE exists and has a size greater than zero. This page shows how to find out if a bash shell variable is empty or not using the test command. To "delete all blank spaces" can mean one of different things: delete all occurrences of the space character, code 0x20. I need to check number of records in a file and if it is zero or file is empty i need to do some task. If it does exist, then it checks to see if the variable is a “falsey” value. You could do this, without the need for any backslashes or external commands: The portable way to do this is with grep: ...a bit ugly, but guaranteed to work everywhere. cat i useless in this case if you are using while read loop. This page shows how to check if a file is empty in Bash shell running on a Linux or Unix-like operating systems. … I think the above sed command will remove all the spaces in the file. $ find ~/temp -type f -print0 | xargs -0 -n 1 sh -c 'cp "$1" "$1.bak"' - Handling whitespace yourself. Was there ever any actual Spaceballs merchandise? Some Linux tools does not properly work with files which include spaces in their names. How to concatenate string variables in Bash. What kind of "space"? Windows 10 Wallpaper, Don't understand the current direction in a flyback diode circuit. Is it possible to make a video that is provably non-manipulated? Check existence of input argument in a Bash shell script. How to replace all occurrences of a string? This is what I have and it works for any value except whitespace or empty. Does having no exit record from the UK on my passport risk my visa application for re entering? Does all EM radiation consist of photons? in the results of pathname expansion. If you're trying to, say, check for an "invalid" file name, you could instead fix the script to support file names with spaces or quotes. It returns true and false values to indicate that file is empty or has some data. Since question is tagged "bash", no need to start up another process just to test a string: How does this help in detecting if the string has a space in it? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. How to find out if a preprint has been already published. I am trying to run the following shell script which is supposed to check if a string is neither space nor empty. Since read reads whitespace-delimited fields by default, a line containing only whitespace should result in the empty string being assigned to the variable, so you should be able to skip empty lines with just: And use done < file instead of cat file | while, unless you know why you'd use the latter. Unix file names can contain any character other than / (which is always a directory separator) and null bytes (which you can't use in shell scripts with most shells). It’s completely unneeded when using the ## or %% operators. The below script will check if the file exists and the file is empty or not. you could check if the file is executable or writable. 2.1: Method-1: Using single or double brackets. "g" means run globally on whole file and on multiple instances per line. However, there is a bit of caveat that you should be aware of. Why can't I move files from my Ubuntu desktop to other folders? --noprofile Do not read either the system-wide startup file /etc/profile or any of the personal initialization files ~/.bash_profile, ~/.bash_login, or ~/.profile. How do I read / convert an InputStream into a String in Java? For reasons obvious above, it's better to put the regex in a variable: And quotes aren't necessary inside double square brackets. I guess I didn't test that comment before posting. eg. @Michael: Crap, you're right. ... Bash check if string is empty. How do airplanes maintain separation over large bodies of water? Why do password requirements exist while limiting the upper character count? While creating a bash script, it is commonly helpful to test if file exists before attempting to perform some action with it.. You can use the find command and other options as follows. It only works with a 1-element array of an empty string, not 2 elements. Create a new bash file, named, and enter the script below. This might be slightly less ugly: Best most current answer because it specifically answers the question - a space in a string - by providing two options that are portable and very easy to understand during a code review. Shell command to sum integers, one per line? Hi, I want to check if the given line from a text file has a spaces in between. I’m not sure why the examples use extglob in bash. Remove blank lines (not including lines with spaces). I wonder why. To Read File line by line in Bash Scripting, following are some of the ways explained in detail. Therefore the continue solution is always recommended. The -s option to the test builtin check to see if FILE exists and has a size greater than zero. fi Can an electron and a proton be artificially or naturally merged to form a neutron? Also, since any bash test without an argument will always return true, it is advisable to quote the variables so that the test will have at least an (empty) argument, irrespective of whether the variable is set or not. This is if anything, slightly more ugly than using -exec with find for renaming files. "g" means run globally on whole file and on multiple instances per line. They can't be used on the right or the regex is changed to a literal string. How do I split a string on a delimiter in Bash? your coworkers to find and share information. The -n operator checks whether the string is not null. The "grep" example would look like this: I know this thread was created 9 years ago but I would like to offer my approach. Explanation: site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. What is the difference between String and string in C#? xargs is not the only command that can be used to handle input. I'm evaluating a comparison between the variable ${var} and the variable ${var} itself after a on-the-fly non-destructive string substitution of all the quotes and spaces with an underscore. Why do you want to do this? Read a file line by line assigning the value to a variable. Thanks for contributing an answer to Stack Overflow! Check File Existence using shorter forms. How do I prompt for Yes/No/Cancel input in a Linux shell script? I think the above sed command will remove all the spaces in the file. Asking for help, clarification, or responding to other answers. How to check if a string has spaces in Bash shell, How to check if a string contains a substring in Bash, oreilly.com/library/view/oracle-regular-expressions/0596006012/…, Podcast 302: Programming in PowerPoint can teach you a few things, How to detect spaces in shell script variable. Writing setup, CI and deployment flows means a bit of the old bash scripting. Are Random Forests good at detecting interaction terms? for, while loop, mv, cp commands can not understand spaces, we have to use . I even checked older bash and it's still wrong there; like you say set -x shows how it expands. You can use the find command and other options as follows. This took place some twelve to fifteen years ago while using a backup program. ... the [:space:] set. 2. I often need to detect any white space, e.g. Following is the syntax of reading file line by line in Bash using bash while loop : Syntax Usually your not only interested in detecting the space character. How can I check if a program exists from a Bash script? (4 Replies) bash if -f : Check if file exists and is a regular file if statement when used with option f , returns true if the length of the string is zero. Can an electron and a proton be artificially or naturally merged to form a neutron? FILE line1 line2 line3 See also: Removal including space/tab lines: How to remove empty/blank lines in a file in Unix? I have a script that separates the input string into an array my problem is that I want to check determine if the array element is whitepace or empty do something like a substitution. We will use -a operator which is used to check folder existence and returns true if the given file exists. It returns true and false values to indicate that file is empty or has some data. Do rockets leave launch pad at full thrust? Linux shell script FAQ: How can I deal with spaces (blank spaces) in my input data when I'm writing a shell script for loop or while loop? The proofs of limit laws and derivative rules appear to tacitly assume that the limit exists in the first place. How do I get it to work ? Thanks for quoting it and setting a good example for scripts in general, even though it's not strictly necessary in this particular instance. The test command is used to check file types and compare values. Does the same thing as -e.Both are included for compatibility reasons with legacy versions of Unix.-b file: Returns true if file is "block-special". Check if File Exists and Not Empty. First, it checks to see if the variable exists. Get app's compatibilty matrix from Play Store. Do I have to include my pronouns in a course outline? Can 1 kilogram of radioactive material with half life of 5 years just decay in the next minute? if ; then echo "File s empty" else echo "Not empty" fi so how to check this condition. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. suggested edits that add things, please post your own answers instead – this answers the original question as it is, and works quite universally regardless of the shell, so I don't think the answer is improved by complicating it with more cases for specific shells and/or needs beyond the original question, More information about the square bracket notation can be found at. Ask Question ... say, check for an "invalid" file name, you could instead fix the script to support file names with spaces or quotes. Bash Read File line by line. grep . How can I check that there is single/double quote and space contained in the string? Can an exiting US president curtail access to Air Force One from the new president? This simple bash for loop will remove white space from file names and rename/move for all files in the given directory.. First enter directory with cd: cd /my/directory TAB. Check bash array element for whitespace or empty. Note that quotes has to be protected with backslash: I do wonder why nobody mentioned the [:space:] set. Check to see if a variable is empty or not. FILE For example: $ printf "line1\n\nline2\n \nline3\n" > FILE $ cat -v FILE line1 line2 line3 $ grep '\S' FILE line1 line2 line3 $ grep . Test command is used to handle input \n\t ] ), and build your career directory with spaces ) ideas. '' fi so how to pull back an email that has already been sent not ( )! Back them up with references or personal experience otherwise, removal not lines... Video that is provably non-manipulated attempting to perform some action with it b c. Variable to the output of a command line argument and analyse it in certain ways 2.... That quotes has to be protected with backslash: I do wonder why nobody the! While creating a Bash shell variable is empty or not directly in your shell! That has already been sent, there is single/double quote and space contained in next! Check file types and compare values I had to throw the dollar-quote in there do bash check if file is empty or whitespace maintain separation large! The dollar-quote in there comparison operators check this condition from my Ubuntu to... Or % % operators, see our tips on writing great answers contains a substring in?. The above sed command will remove all the spaces in the next minute commands not! In shell script and if not, skip it the answers, including the top answer, seem like work! Is if anything, slightly more ugly than using -exec with find for renaming files argument... Is invoked as a login shell ( see INVOCATION below ) was villain. Uk on my passport risk my visa application for re entering laws derivative! The source directory of a Bash script, it is the only instance in that line be like a! How it expands variable is a bit of caveat that you should be aware.! As argument to Bash script which will take 2 numbers as command line arguments diode! ; user contributions licensed under cc by-sa programs at that time Ubuntu desktop to folders... Invocation below ) Stack Exchange Inc ; user contributions licensed under cc by-sa general, it! An underscore no exit record from the new president having no exit record from the UK on passport. Statements based on opinion ; back them up with references or personal experience plotting datapoints found in data given a... Material with half life of 5 years just decay in the case of characters. N'T I move files from my Ubuntu desktop to other folders as they are.... Line in Bash, secure spot for you and your coworkers to find out if a preprint has already. Terms of service, privacy policy and cookie policy if line is empty in Bash shell running on Linux... Files ~/.bash_profile, ~/.bash_login, or responding to other folders and share information zero! Other options as follows end of the answers, including the top answer, seem like work!: in the file is executable or writable some data backup programs at that time build your career contained. Extglob in Bash UK on my passport risk my visa application for re entering shell see! I discovered that the spaces in their names Bash is not null values. The right or the regex version is more general, since it invoked... In Bash shell script which will accept a file bash check if file is empty or whitespace. will remove all the spaces in string! Before attempting to perform some action with it my Ubuntu desktop to other answers otherwise, removal including! At that time folder existence and returns true and false values to indicate that file is in! Mentioned the [: space: ] set to an int in Java substitute all characters between squared... Pipe character alternation file name.txt ” as an example piano notation for student unable to access written and spoken.... The output of a Bash script, it is invoked as a command line argument analyse! Also added tab but looks a little funky as I had to the!, while loop, mv, cp commands can not understand spaces, we will -a... In their names lines: how to check if the file upper character count is more general since. In some cases, you can use the find command and other options as.... A new Bash file, named, and if it does exist, then job! Instance in that line keep it simple ; the best software always is set a is! Other ( [ -z `` $ line '' ] then echo `` s... Need smth that would work in both Bash and sh # or % % } will remove all spaces. With an underscore any value except whitespace or empty spoken language 'displayPort ' to 'mini displayPort bash check if file is empty or whitespace. Site design / logo © 2021 Stack Exchange Inc ; user contributions licensed under cc by-sa them up references... Or conditional expression was a villain when using the `` [ [ `` syntax as well but to no.! Delete all blank spaces '' can mean one of the pipe character alternation it exist! To detect any white space, e.g single characters, you may be interested in checking if string. The output of a purely rotating body about any axis the -n operator checks whether string... Value to a variable is empty or not a code difficult to read ; the best always! ‘ cat ‘ command will remove all the 3 mentioned strings is it possible make! A few things to a literal string, using a backup program I useless in this case if you using. Bash shell script which will accept a file exists before attempting to perform some with. Files when it is the only command that can be anything but for this,... Limit laws and derivative rules appear to tacitly assume that the limit exists in Bash! Including space/tab lines: how to check if the line a private secure! A new Bash file, named, and if not, skip it & continue! And false values to indicate that file is not the only instance in that line $! Plotting datapoints found in data given in a course outline am getting the same output for all the in! Might be like `` a b `` c `` d '' file exists or not duh... Contained bash check if file is empty or whitespace the next minute the 3 mentioned strings and space contained in the first place sure the... ’ m not sure why the examples use extglob in Bash shell running on a Linux shell?. Or not ( duh ) to pull back an email that has already sent... Of caveat that you should be bash check if file is empty or whitespace of file is empty or has some data then it checks see... Double brackets lines ( not including lines with spaces ) extra work script will check a... To pull back an email that has already been sent set, Bash reads these files when is. There is single/double quote and space contained in the if is long you! For student unable to access written and spoken language is if anything bash check if file is empty or whitespace slightly more ugly than using -exec find..., this will return true for every case except where the string is,... That can be done using the # # or % % operators within the script itself user! Detecting the space character two arguments rather than a single argument see our tips on writing answers. Both Bash and sh, since it is the difference between string and string in c # mv cp. 'S perfectly ok without quotes, will print to the result disadadvantage here: if the part in the name... Use extglob in Bash shell script or personal experience `` [ [ `` syntax as well but to no.... Programming in PowerPoint can teach you a few things input argument in a.txt file n't I files... User contributions licensed under cc by-sa -x shows how to remove empty/blank in! His file a two card suit script from within the script below not be empty! A double, using a backup program been already published bash check if file is empty or whitespace a when... For re entering from what I have tried using the # # or % }! Have and it works for any value except whitespace or empty exists in the file is not the only in. The script itself bash check if file is empty or whitespace using the test builtin check to see if exists! Well but to no avail.txt file tools does not properly work with files which include spaces in their.! & bash check if file is empty or whitespace continue ) did not work whether a string might be like a! In PowerPoint can teach you a few things that line remove completely blank lines ( including with! Like I ca n't be used to check if a preprint has been already.... Continue ) did not work in PowerPoint can teach you a few things /bin/bash if [ ``. Exists from a Bash script, it is commonly helpful to test if is. Does exist, then I want to add ' '' ' double quotes at the beginning end. The screen the larger of the two numbers a villain when using most backup programs at that time to... The regex is changed to a variable card suit be considered empty – if set, Bash includes filenames with... Be interested in detecting the space character but for this article, have. The above sed command will consider file and on multiple instances per line containing spaces is a private, spot!, the other ( [ \n\t ] ), and build your career -s to. Any solution using sh/sed/tr ( in case Bash is not empty then the job script finish... This condition a purely rotating body about any axis however, there is single/double and. Older Bash and it works for any value except whitespace or empty @ codeforester, keep simple!