Split output of command by columns using Bash

Question

I want to do this     run a command capture the output select a line select a column of that line   Just as an example  let s say I want to get the command name from a  PID  please note this is just an example  I m not suggesting this is the easiest way to get a command name from a process id - my real problem is with another command whose output format I can t control    If I run ps I get       PID TTY          TIME CMD 11383 pts 1    00 00 00 bash 11771 pts 1    00 00 00 ps    Now I do ps   egrep 11383 and get   11383 pts 1    00 00 00 bash  Next step  ps   egrep 11383   cut -d    -f 4  Output is    lt absolutely nothing  gt    The problem is that cut cuts the output by single spaces  and as ps adds some spaces between the 2nd and 3rd columns to keep some resemblance of a table  cut picks an empty string  Of course  I could use cut to select the 7th and not the 4th field  but how can I know  specially when the output is variable and unknown on beforehand

User · Answer

Similar to brianegge s awk solution  here is the Perl equivalent   ps   egrep 11383   perl -lane  print  F 3     -a enables autosplit mode  which populates the  F array with the column data  Use -F  if your data is comma-delimited  rather than space-delimited   Field 3 is printed since Perl starts counting from 0 rather than 1

User · Answer

Your command  ps   egrep 11383   cut -d    -f 4   misses a tr -s to squeeze spaces  as unwind explains in his answer   However  you maybe want to use awk  since it handles all of these actions in a single command   ps   awk   11383   print  4     This prints the 4th column in those lines containing 11383  If you want this to match 11383 if it appears in the beginning of the line  then you can say ps   awk    11383   print  4

User · Answer

Please note that the tr -s     option will not remove any single leading spaces  If your column is right-aligned  as with ps pid        ps h -o pid user -C ssh sshd   tr -s      1543 root 19645 root 19731 root   Then cutting will result in a blank line for some of those fields if it is the first column      lt previous command gt    cut -d     -f1  19645 19731   Unless you precede it with a space  obviously     lt command gt    sed -e  s      amp      tr -s       Now  for this particular case of pid numbers  not names   there is a function called pgrep     pgrep ssh   Shell functions  However  in general it is actually still possible to use shell functions in a concise manner  because there is a neat thing about the read command      lt command gt    while read a b  do echo  a  done   The first parameter to read  a  selects the first column  and if there is more  everything else will be put in b  As a result  you never need more variables than the number of your column  1   So    while read a b c d  do echo  c  done   will then output the 3rd column  As indicated in my comment     A piped read will be executed in an environment that does not pass variables to the calling script   out   ps whatever     read a b c d  echo  c      arr    ps whatever     read a b c d  echo  c  b      echo   arr 1         will output  b     The Array Solution  So we then end up with the answer by  frayser which is to use the shell variable IFS which defaults to a space  to split the string into an array  It only works in Bash though  Dash and Ash do not support it  I have had a really hard time splitting a string into components in a Busybox thing  It is easy enough to get a single component  e g  using awk  and then to repeat that for every parameter you need  But then you end up repeatedly calling awk on the same line  or repeatedly using a read block with echo on the same line  Which is not efficient or pretty  So you end up splitting using    name      and so on  Makes you yearn for some Python skills because in fact shell scripting is not a lot of fun anymore if half or more of the features you are accustomed to  are gone  But you can assume that even python would not be installed on such a system  and it wasn t  -

User · Answer

One easy way is to add a pass of tr to squeeze any repeated field separators out     ps   egrep 11383   tr -s       cut -d     -f 4

User · Answer

I think the simplest way is to use awk   Example     echo  11383 pts 1    00 00 00 bash    awk    print  4     bash

User · Answer

try  ps   amp  while read -p first second third fourth etc   do    if     first     11383        then        echo got   fourth    fi        done

User · Answer

Instead of doing all these greps and stuff  I d advise you to use ps capabilities of changing output format   ps -o cmd  -p 12345   You get the cmmand line of a process with the pid specified and nothing else   This is POSIX-conformant and may be thus considered portable

User · Answer

Bash s set will parse all output into position parameters    For instance  with set   free -h  command  echo  7 will show  Mem

User · Answer

Using array variables  set   ps   egrep   11383     echo  4   or   A     ps   egrep   11383        echo   A 3

User · Answer

Getting the correct line  example for line no  6  is done with head and tail and the correct word  word no  4  can be captured with awk   command head -n 6 tail -n 1 awk   print  4

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