Sponsored Content
Top Forums Shell Programming and Scripting compare variable against regular expression? Post 302198036 by era on Thursday 22nd of May 2008 06:20:17 AM
Old 05-22-2008
The if command simply evaluates another command, and examines its exit code to decide whether to take the then branch or the else branch (if present). You can use the expr command to match a string against a regular expression, or echo | grep. I would recommend case for this, though, even if it actually uses glob expressions, not true regular expressions.

Some shells also have built-in regex operators with the [[ conditional ]] syntax.

Code:
if echo "$var" | grep '[^0-9]'; then
  echo not a number  
fi
if expr "$var" : '[^0-9]' >/dev/null; then
  echo not a number
fi
case $var in
  *[!0-9]*) echo not a number;;    # not a regex proper
esac
if [[ "$var" =~ [^0-9] ]] ; then
  echo not a number
fi

All of these are more or less functionally equivalent. (They will not reject an empty string as not a number; implementing that is left as an exercise.)

Last edited by era; 05-22-2008 at 07:23 AM.. Reason: Will accept empty string as well as numbers, actually
 

10 More Discussions You Might Find Interesting

1. Shell Programming and Scripting

regular expression using a variable

hello, I use AIX with ISM PILOT, I want to match something with a varible like this : $variable = 10 #this variable is the number of the job "$variable STARTED" # the pattern how can use this variable to match it with the word STARTED Tanks (0 Replies)
Discussion started by: barribar
0 Replies

2. Shell Programming and Scripting

Awk's variable in regular expression

Anyone know how I will use awk's variable in a regular expression? This line of code of mine is working, the value PREMS should be a variable: awk '$1 ~ /PREMS/ { if(length(appldata)+2 >= length($1)) print $0; }' appldata=$APPLDATA /tmp/file.tmp The value of APPLDATA variable is PREMS. ... (2 Replies)
Discussion started by: Orbix
2 Replies

3. Shell Programming and Scripting

AWK - compare $0 to regular expression + variable

Hi, I have this script: awk -v va=45 '$0~va{print}' flo2 That returns: "4526745 1234 " (this is the only line of the file "flo2". However, I would like to get "va" to match the begining of the line, so that is "va" is different than 45 (eg. 67, 12 ...) I would not have any output. That... (3 Replies)
Discussion started by: jolecanard
3 Replies

4. Shell Programming and Scripting

Passing Variable to Regular Expression

Hi All, Below is a sample code: print "Enter the Name: "; my $Name = <>; print "Word is $Name"; open (FH,"AIDNameList.txt"); while (<FH>) { my $line; print "Word is $Name"; for $line(<FH>)... (12 Replies)
Discussion started by: jisha
12 Replies

5. Shell Programming and Scripting

How to compare a file name with a regular expression !!

Hi, I need to compare file names in a folder with several strings(which are in regular expression format): For example: there is a file "objectMyHistoryBook" and there are several strings to compare this file name with: objectMyMaths*, objectMyEnglish*, objectMyHistory*,... (2 Replies)
Discussion started by: Lucifer_123
2 Replies

6. Programming

Perl: How to read from a file, do regular expression and then replace the found regular expression

Hi all, How am I read a file, find the match regular expression and overwrite to the same files. open DESTINATION_FILE, "<tmptravl.dat" or die "tmptravl.dat"; open NEW_DESTINATION_FILE, ">new_tmptravl.dat" or die "new_tmptravl.dat"; while (<DESTINATION_FILE>) { # print... (1 Reply)
Discussion started by: jessy83
1 Replies

7. UNIX for Dummies Questions & Answers

grep with variable and regular expression

i have a command line like this in csh script grep -i "$argv$" which i wanted to select the line ending with string provided as argument but it couldn't interpret the '$' (ending with).. any help? (3 Replies)
Discussion started by: ymc1g11
3 Replies

8. UNIX for Dummies Questions & Answers

Compare files with regular expression

Readers, Reading a previous post about comparing files using awk ('awk-compare-2-columns-2-files-output-whole-line', https://www.unix.com/shell-programming-scripting/168432-awk-compare-2-columns-2-files-output-whole-line.html), it is possible to adjust this, so that regular expression can be used... (8 Replies)
Discussion started by: linuxr
8 Replies

9. Shell Programming and Scripting

Regular expression as a variable

I'm trying to use a series of regular expressions as variables but can't get it to behave properly. You can see below what I'm trying to do. Here with lowercase a-z and the same with uppercase, numbers 0-9 and again with a set of special characters, without having to type out every single... (3 Replies)
Discussion started by: 3therk1ll
3 Replies

10. Shell Programming and Scripting

How to store regular expression in a variable?

Hi, Im facing a weird behavior storing regular expression in a vaiable. Let us consider >file_name=CTP02_*.tar when I echo the above variable its displaying below which is file CTP02_*tar but when I create a file with name CTP02_1234.tar, and when I echo $file_name its showing... (3 Replies)
Discussion started by: rdineshredy
3 Replies
REGEX(3)						     Library Functions Manual							  REGEX(3)

NAME
re_comp, re_exec - regular expression handler SYNOPSIS
char *re_comp(s) char *s; re_exec(s) char *s; DESCRIPTION
Re_comp compiles a string into an internal form suitable for pattern matching. Re_exec checks the argument string against the last string passed to re_comp. Re_comp returns 0 if the string s was compiled successfully; otherwise a string containing an error message is returned. If re_comp is passed 0 or a null string, it returns without changing the currently compiled regular expression. Re_exec returns 1 if the string s matches the last compiled regular expression, 0 if the string s failed to match the last compiled regular expression, and -1 if the compiled regular expression was invalid (indicating an internal error). The strings passed to both re_comp and re_exec may have trailing or embedded newline characters; they are terminated by nulls. The regular expressions recognized are described in the manual entry for ed(1), given the above difference. SEE ALSO
ed(1), ex(1), egrep(1), fgrep(1), grep(1) DIAGNOSTICS
Re_exec returns -1 for an internal error. Re_comp returns one of the following strings if an error occurs: No previous regular expression, Regular expression too long, unmatched (, missing ], too many () pairs, unmatched ). 3rd Berkeley Distribution May 15, 1985 REGEX(3)
All times are GMT -4. The time now is 12:20 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy