How to process each output line in a loop

Question

I have a number of lines retrieved from a file after running the grep command as follows   var  grep xyz abc txt    Let   s say I got 10 lines which consists of xyz as a result   Now I need to process each line I got as a result of the grep command  How do I proceed for this

User · Accepted Answer

One of the easy ways is not to store the output in a variable, but directly iterate over it with a while/read loop.

Something like:

grep xyz abc.txt | while read -r line ; do
    echo "Processing $line"
    # your code goes here
done

There are variations on this scheme depending on exactly what you're after.

If you need to change variables inside the loop (and have that change be visible outside of it), you can use process substitution as stated in fedorqui's answer:

while read -r line ; do
    echo "Processing $line"
    # your code goes here
done < <(grep xyz abc.txt)

User · Answer

I would suggest using awk instead of grep   something else here   awk   0  xyz     your code goes here   abc txt

User · Answer

Without any iteration with the --line-buffered grep option   your command   grep --line-buffered  your search    Real life exemple with a Symfony PHP Framework router debug command ouput  to grep all  api  related routes   php bin console d r   grep --line-buffered  api

User · Answer

For those looking for a one-liner   grep xyz abc txt   while read -r line  do echo  Processing  line   done

User · Answer

Often the order of the processing does not matter  GNU Parallel is made for this situation   grep xyz abc txt   parallel echo do stuff to      If you processing is more like   grep xyz abc txt   myprogram reading from stdin   and myprogram is slow then you can run   grep xyz abc txt   parallel --pipe myprogram reading from stdin

User · Answer

Iterate over the grep results with a while read loop  Like   grep pattern filename txt   while read -r line   do     echo  Matched Line    line        your code goes here done

User · Answer

You can do the following while read loop  that will be fed by the result of the grep command using the so called process substitution   while IFS  read -r result do      whatever with value  result done  lt   lt  grep  xyz  abc txt    This way  you don t have to store the result in a variable  but directly  inject  its output to the loop     Note the usage of IFS  and read -r according to the recommendations in BashFAQ 001  How can I read a file  data stream  variable  line-by-line  and or field-by-field        The -r option to read prevents backslash interpretation  usually used   as a backslash newline pair  to continue over multiple lines or to   escape the delimiters   Without this option  any unescaped backslashes   in the input will be discarded  You should almost always use the -r   option with read       In the scenario above IFS  prevents trimming of leading and trailing   whitespace  Remove it if you want this effect    Regarding the process substitution  it is explained in the bash hackers page      Process substitution is a form of redirection where the input or   output of a process  some sequence of commands  appear as a temporary   file

[bash] How to process each output line in a loop?

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