What is the meaning of ## in UNIX shell script?

Shell Programming and Scripting
1

Hi All,

I am new to unix shell scripting and I was documenting one of the unix script and encountered below statements -

for ii in `ls -1rt /oracle/admin/MARSCOPY/ext_files/fpm-ifpm/*.small.txt | tail -1 | awk '{print $1}'`
do
smallssim=${ii##/oracle/admin/MARSCOPY/ext_files/fpm-ifpm/}
prefix=`echo $smallssim | awk -F. '{print $1}'`

I tried to find the meaning of ## on google or other posts but could not find it.

Can anyone please help me understand meaning of the value smallssim?

Thanks in Advance.
Jay Shukla

2

Hello shuklajayb4,

Welcome to forums, hope you will enjoy learning here. It is called Parameter expansion, when you do a man bash you could see the following.

Here is an example of same too.
So let's say we have following string into a variable.

MYSTRING="Be liberal in what you accept, and conservative in what you send"

So here is the use of # and ## .

${MYSTRING#* }	Be liberal in what you accept, and conservative in what you send
${MYSTRING##* }	Be liberal in what you accept, and conservative in what you send

As you could see above(selected text will not be shown) # is removing the text till very first space and on other hand ## is printing the text till very last(maximum) match of space. I hope this helps you.

Thanks,
R. Singh

2 Likes
3

Thanks Ravinder !! This helps to understand it better.