How to use regex in if-statement in shell script? ( transformation from bash script to regular shell script)

Question

I've been writing a script with #!/bin/bash shebang for a school project but I found out few hours ago that the shebang has to be #!/bin/sh. Could you advise me how to format the second if-condition so it would be compatible for every shell script?

if [[ -z $date ]]; then
   echo "No date argument"
   exit 1
elif [[ $date =~ ^[0-9]{4}-[0-9]{2}-[0-9]{2}$ ]]; then
   return

Actually, it is best to write if [ -z "$date" ]: if $date is really empty, without double quotes it will fail. And there is no need of double brackets in this comparison. — Dario
– Dario, Commented Mar 24, 2018 at 21:21

Cyrus · Accepted Answer · 2018-03-24 21:23:14Z

3

With GNU grep.

Replace

[[ $date =~ ^[0-9]{4}-[0-9]{2}-[0-9]{2}$ ]]

with

echo "$date" | grep -q -E '^[0-9]{4}-[0-9]{2}-[0-9]{2}$'

or use

echo "$date" | egrep '^[0-9]{4}-[0-9]{2}-[0-9]{2}$' >/dev/null

edited Mar 24, 2018 at 21:23

answered Mar 24, 2018 at 21:12

Cyrus

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