Searching for pattern in variable using case statements

Shell Programming and Scripting
1

i would like to search a variable for a pattern, without having make any calls to external tools.

i have a code like this:

COUNTPRO2="gine is very bad
vine is pretty good"

case "${COUNTPRO2}" in
*vine*)
    factor=${COUNTPRO2}
    echo $factor
;;
esac

If the variable contains a specific pattern, i.e. in this case "vine", then i want the case statement to output ONLY the line containing the pattern..i.e.

vine is pretty good

is this possible?

what i was doing before was:

factor=$(echo "${COUNTPRO2}" | egrep vine)

I would like to avoid calling the egrep.

the solution needs to be portable as i intend to use it on linux, aix and sunos

2

Hi.

It would probably be useful if you were to tell us which items the different platforms had in common: bash, ksh, zsh, awk, perl, grep , etc.

Here's a solution using an array, loop, and case:

#!/usr/bin/env bash

# @(#) s1       Demonstrate shell array with case selector.

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
# export PATH="/usr/local/bin:/usr/bin:/bin"
LC_ALL=C ; LANG=C ; export LC_ALL LANG
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { : ; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
C=$HOME/bin/context && [ -f $C ] && $C

v1="gine is very bad
vine is pretty good"

pl " Input data variable, piped into cat:"
echo "$v1" | cat -n

pl " Input data array with printf:"
declare -a a1="$v1"
printf "%s\n" "${a1[*]}"

pl " Looking through each element in the array:"
IFS=$'\n'
for line in ${a1[*]}
do
  db " Working on line [$line]"
  case $line in
  (*vine*)      echo " HIT! Found vine." ;;
  esac
done

exit 0

producing:

$ ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 3.16.0-4-amd64, x86_64
Distribution        : Debian 8.4 (jessie) 
bash GNU bash 4.3.30

-----
 Input data variable, piped into cat:
     1  gine is very bad
     2  vine is pretty good

-----
 Input data array with printf:
gine is very bad
vine is pretty good

-----
 Looking through each element in the array:
 db,  Working on line [gine is very bad]
 db,  Working on line [vine is pretty good]
 HIT! Found vine.

See man bash , etc. for details.

Best wishes ... cheers, drl

1 Like
3

they have awk in common.

4

What about a while loop?

COUNTPRO2="gine is very bad
vine is pretty good"

echo "${COUNTPRO2}" | while read line; do
        [[ $line == *"vine"* ]] && echo $line
done
1 Like
5

this seems to do precisely what i needed. not sure how much time it'll save as oppose to calling grep for each pattern i'm searching for.

6

It would all depend upon the number of lines the code is traversing.

7

You could also try:

#!/bin/ksh
COUNTPRO2="gine is very bad
vine is pretty good"

while IFS= read -r factor
do	case "$factor" in
	(*vine*)printf '%s\n' "$factor"
		;;
	esac
done <<EOF
$COUNTPRO2
EOF

Note that I used printf instead of echo because the output you get from echo might not be what you want if a line in the expansion of $COUNTPRO2 starts with a hyphen or contains any backslash characters. And, using a here-document instead of an array makes it portable to many more shells.

Forking and execing an external utility is a VERY slow operation when compared to the actions required to perform a case statement pattern match.

Although the above was written and tested using a Korn shell, this should work with any shell that is based on Bourne shell syntax (including a 1970's vintage pure Bourne shell).

2 Likes
8

Old Bourne shells do not like ( ) in a case selector, and no -r for read.

#!/bin/sh
COUNTPRO2="gine is very bad
vine is pretty good"

while IFS= read factor
do
    case "$factor" in
    *vine*)
        printf '%s\n' "$factor"
    ;;
    esac
done <<EOF
$COUNTPRO2
EOF

A here-document uses a /tmp file. Another method is a pipe to the while loop

#!/bin/sh
COUNTPRO2="gine is very bad
vine is pretty good"

printf '%s\n' "$COUNTPRO2" |
while IFS= read factor
do
    case "$factor" in
    *vine*)
        printf '%s\n' "$factor"
    ;;
    esac
done
1 Like