How do I compare strings in Bourne Shell?

Question

I need to compare strings in shell:

var1="mtu eth0"

if [ "$var1" == "mtu *" ]
then
    # do something
fi

But obviously the "*" doesn't work in Shell. Is there a way to do it?

Answer 1

Use the Unix tools. The program cut will happily shorten a string.

if [ "$(echo $var1 | cut -c 4)" = "mtu " ];

... should do what you want.

Answer 2

bash

Shortest fix:

if [[ "$var1" = "mtu "* ]]

Bash's [[ ]] doesn't get glob-expanded, unlike [ ] (which must, for historical reasons).

---

bash --posix

Oh, I posted too fast. Bourne shell, not Bash...

if [ "${var1:0:4}" == "mtu " ]

${var1:0:4} means the first four characters of $var1.

---

/bin/sh

Ah, sorry. Bash's POSIX emulation doesn't go far enough; a true original Bourne shell doesn't have ${var1:0:4}. You'll need something like mstrobl's solution.

if [ "$(echo "$var1" | cut -c0-4)" == "mtu " ]