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How do I write and match regex in / bin / sh script?

I'm writing a shell script for a limited unix-based microkernel that doesn't have bash! For some reason / bin / sh cannot run the following lines.

if [[ `uname` =~ (QNX|qnx) ]]; then
read -p "what is the dev prefix to use? " dev_prefix
if [[ $dev_prefix =~ ^[a-z0-9_-]+@[a-z0-9_-"."]+:.*$ ]]; then

For 1st and 3rd lines, it complains about a missing expression statement, and for 2nd line, it doesn't talk about coprocess! Can anyone shed some light on the differences between the / bin / bash and / bin / sh scripts?

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2 answers


You can use this script equivalent in /bin/sh

:



if uname | grep -Eq '(QNX|qnx)'; then
   printf "what is the dev prefix to use? "
   read dev_prefix
   if echo "$dev_prefix" | grep -Eq '^[a-z0-9_-]+@[a-z0-9_-"."]+:'; then
   ...
   fi
fi
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Here's a way to see what non-Posix functions are in the script:

Copy / Paste this to shellcheck.net:

#!/bin/sh
if [[ `1uname` =~ (QNX|qnx) ]]; then
  read -p "what is the dev prefix to use? " dev_prefix
  if [[ $dev_prefix =~ ^[a-z0-9_-]+@[a-z0-9_-"."]+:.*$ ]]; then
    : nothing
  fi
fi


Or install shellcheck locally and run shellcheck ./check.sh

it and it will highlight non-list functions:

In ./check.sh line 2:
if [[ `1uname` =~ (QNX|qnx) ]]; then
   ^-- SC2039: In POSIX sh, [[ ]] is not supported.
      ^-- SC2006: Use $(..) instead of deprecated `..`

In ./check.sh line 4:
  if [[ $dev_prefix =~ ^[a-z0-9_-]+@[a-z0-9_-"."]+:.*$ ]]; then
     ^-- SC2039: In POSIX sh, [[ ]] is not supported.

You need to either rewrite the expressions as globes (not realistic) or use external commands (grep / awk) explained by @anubhava

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