bash shortest way to get n-th column of output

Question

Let s say that during your workday you repeatedly encounter the following form of columnized output from some command in bash  in my case from executing svn st in my Rails working directory            changes patch M       app models superman rb A       app models superwoman rb   in order to work with the output of your command - in this case the filenames - some sort of parsing is required so that the second column can be used as input for the next command   What I ve been doing is to use awk to get at the second column  e g  when I want to remove all files  not that that s a typical usecase     I would do   svn st   awk   print  2     xargs rm   Since I type this a lot  a natural question is  is there a shorter  thus cooler  way of accomplishing this in bash   NOTE  What I am asking is essentially a shell command question even though my concrete example is on my svn workflow  If you feel that workflow is silly and suggest an alternative approach  I probably won t vote you down  but others might  since the question here is really how to get the n-th column command output in bash  in the shortest manner possible  Thanks

User · Answer

Because you seem to be unfamiliar with scripts, here is an example.

#!/bin/sh
# usage: svn st | x 2 | xargs rm
col=$1
shift
awk -v col="$col" '{print $col}' "${@--}"

If you save this in ~/bin/x and make sure ~/bin is in your PATH (now that is something you can and should put in your .bashrc) you have the shortest possible command for generally extracting column n; x n.

The script should do proper error checking and bail if invoked with a non-numeric argument or the incorrect number of arguments, etc; but expanding on this bare-bones essential version will be in unit 102.

Maybe you will want to extend the script to allow a different column delimiter. Awk by default parses input into fields on whitespace; to use a different delimiter, use -F ':' where : is the new delimiter. Implementing this as an option to the script makes it slightly longer, so I'm leaving that as an exercise for the reader.

Usage

Given a file file:

1 2 3
4 5 6

You can either pass it via stdin (using a useless cat merely as a placeholder for something more useful);

$ cat file | sh script.sh 2
2
5

Or provide it as an argument to the script:

$ sh script.sh 2 file
2
5

Here, sh script.sh is assuming that the script is saved as script.sh in the current directory; if you save it with a more useful name somewhere in your PATH and mark it executable, as in the instructions above, obviously use the useful name instead (and no sh).

User · Answer

I found myself in the same situation and ended up adding these aliases to my  profile file   alias c1  awk   print   1    alias c2  awk   print   2    alias c3  awk   print   3    alias c4  awk   print   4    alias c5  awk   print   5    alias c6  awk   print   6    alias c7  awk   print   7    alias c8  awk   print   8    alias c9  awk   print   9      Which allows me to write things like this   svn st   c2   xargs rm

User · Answer

It looks like you already have a solution  To make things easier  why not just put your command in a bash script  with a short name  and just run that instead of typing out that  long  command every time

User · Answer

If you are ok with manually selecting the column  you could be very fast using pick   svn st   pick   xargs rm   Just go to any cell of the 2nd column  press c and then hit enter

User · Answer

To accomplish the same thing as   svn st   awk   print  2     xargs rm   using only bash you can use   svn st   while read a b  do rm   b   done   Granted  it s not shorter  but it s a bit more efficient and it handles whitespace in your filenames correctly

User · Answer

You can use cut to access the second field   cut -f2   Edit  Sorry  didn t realise that SVN doesn t use tabs in its output  so that s a bit useless  You can tailor cut to the output but it s a bit fragile - something like cut -c 10-  would work  but the exact value will depend on your setup   Another option is something like  sed  s   s

User · Answer

Note  that file path does not have to be in second column of svn st output  For example if you modify file  and modify it s property  it will be 3rd column    See possible output examples in   svn help st   Example output    M     wc bar c A      wc qax c   I suggest to cut first 8 characters by   svn st   cut -c8-   while read FILE  do echo whatever with   FILE   done   If you want to be 100  sure  and deal with fancy filenames with white space at the end for example  you need to parse xml output   svn st --xml   grep -o  path         sed  s  path      s         Of course you may want to use some real XML parser instead of grep sed

User · Answer

Try the zsh  It supports suffix alias  so you can define X in your  zshrc to be  alias -g X    cut -d    -f2    then you can do   cat file X   You can take it one step further and define it for the nth column   alias -g X2    cut -d    -f2  alias -g X1    cut -d    -f1  alias -g X3    cut -d    -f3    which will output the nth column of file  file   You can do this for grep output or less output  too  This is very handy and a killer feature of the zsh   You can go one step further and define D to be   alias -g D   xargs rm    Now you can type   cat file X1 D   to delete all files mentioned in the first column of file  file     If you know the bash  the zsh is not much of a change except for some new features    HTH Chris

[bash] bash: shortest way to get n-th column of output

Usage

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