How to substitute the output of a grep in Bash?
Check command substitution in the bash man page. You can you back ticks “ or $ () , and personally I prefer the latter. will substitute the output of whoami as the argument for the -e flag of the grep command and the output of the whole command will be line number in /etc/passwd of the running user.
How to do a while read in grep?
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: This way, you don’t have to store the result in a variable, but directly “inject” its output to the loop.
How to grep and execute command ( for every match )?
Have Fun!!! grep may need –line-buffered option to emit each matching line when it matches it, otherwise it buffers up to 4K byte before printing match lines, which defeats the goal here, e.g. tail -f source | grep –line-buffered “expression | xargs
How to avoid using for line in grep file foo?
Avoid using for line in `grep file foo` which is similar, because for always breaks on spaces and this becomes a nightmare for reading lists of files: find . -iname “*blah*.dat” | while read filename; do ….
How to get output of grep in single line?
That is, you can change this: and add an echo command after the loop completes. The $ (…) notation sets up a “command substitution”: the command grep “$a” replaced.txt | cut -f 2 -d” ” is run in a subshell, and its output, minus any trailing newlines, is substituted into the argument-list.
How to send the output of a command?
Surrounding a command in ` marks makes it execute the command and send the output into the command it’s wrapped in. the -v creates an awk variable called me and populates it with your user name. the -F sets the field separator to : as befits the password file.
How to give a line number in Bash?
Give the line number of the file “/etc/passwd” where the information about your own login is. Suppose USERNAME is my own login ID, I was able to do it perfectly in this way: Which simply gave the line number required (there may be a more optimised way).
How to grep logs based on timestamp?
I need logs only from 09:36 to 09:39 in server logs where the timestamp is 2019-03-19T09:37:19 like this. Can anyone suggest me grep command for this