Shell programing and regular expressiong: -> grep

Posted on 2003-11-24
Medium Priority
Last Modified: 2010-04-22
Ok, what I need to do is: list all files in a given directory with a given extension

$1 = directory
$2 = extension

I want to use regular expression for this, so I used the command
filelist = `ls $1 | grep '.*[\\\\.]$2$'`

the problem is, the $ from $2 conflicts with the $ from the regular expression

What I've already tried:
- putting the command in a dummy variable as a string and then execute it
- putting all sort of quotes around it
- banging my head on the table

PS: it works if I replace $2 with the actual extension
This is a school assignment so I can't use any other language or so

Hope someone can help me,


Question by:FrEaK85
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Accepted Solution

glassd earned 750 total points
ID: 9812215
Why not just use:
filelist=`ls $1/*.$2`

More efficient than calling another process (grep).
LVL 24

Expert Comment

ID: 9812773
filelist = `ls $1 | grep ".*[\\\\.]$2$''`
LVL 24

Expert Comment

ID: 9812789
also after setting $1 and $2, do not forget to export them.
and run the above command, it is working onmy system.
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LVL 24

Expert Comment

ID: 9813416
did ot work, please update.

Expert Comment

ID: 9816928

Still don't see why you need to invoke grep when ls was written to do what you want.

Expert Comment

ID: 9817169
try it using eval before grep as follows


filelist=`ls | eval grep '.*[\\\\.]$var2$'`

I think, this  should work

LVL 38

Expert Comment

ID: 9822102
You don't need to use grep, just simply use:

filelist=`/bin/ls ${1}/*.${2}`

PS: use the full path to ls (do a which ls to find out), in case you have
      set aliase for ls.

LVL 20

Expert Comment

ID: 9822293
Actually, there's no need to use 'ls', either. Expanding wildcards (sometimes called globbing) is something the shell does and in all of these formulations using ls, it's really the shell doing the work.

filelist=$(echo $1/*.$2)

As for the way to get your original formulation to work, you need to protect the $ that was intended to be an end-of-string marker from being prematurely taken by the shell as a variable substitution. You seemed to have some concept of this given the number of backslashes you put before that . in the square brackets...but here's a version that worked for me:

filelist=`ls $1 | egrep ".*\\.$2\$"`

The various shells differ a bit in whether variable interpolation takes place inside single quotes inside backticks. To be safe, I stuck to double-quotes.


Author Comment

ID: 9825273
filelist=`ls $1/*.$2` => feeling stupid stupid stupid

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