Shell Programming and Scripting

Code:

echo 'abc_lifecycle.log
  bcde_enjoy.log
  abc_twinkle.log' | awk -F [_.] '{ print $2 }'

basename abc_lifecycle.log .log
abc_lifecycle

Apart from the fact that that is not what the OP asked for, the basename command is entirely unnecessary in a POSIX shell (which is available on every system made in the last 10 to 15 years at least) and on any system before that which had ksh.

Code:

string=abc_lifecycle.log
temp=${string##*_}
printf "%s\n" "${temp%.*}"

If there are many names to be processed, then the awk script I posted previously may be quicker.

echo abc_lifecycle.log | sed 's/\..*$//'

var=abc_lifecycle.log
echo ${var/%.*/}

Code:

$ echo ${var/%.*/}
Syntax error: Bad substitution

When using non-standard syntax, you should specify where it does work. That line will work in bash and ksh93.