CODEWITHSUNDEEP
bashpipe
sugo
sugo

Reputation: 57

Problem with temporary unnamed pipe in bash script

I have the following question:

When I execute the following script directly in a terminal window, the commands behave as expected.

$ diff <(echo tmp) <(echo tmp1)
1c1
< tmp
---
> tmp1

However when I write the same command in a shell script

#! /bin/bash
diff <(echo tmp) <(echo tmp1)

I get the following error message:

$ sh test.sh
test.sh: line 2: syntax error near unexpected token `('
test.sh: line 2: ` diff <(echo tmp) <(echo tmp1)'

Initially I thought this was an issue with diff, but this also happens with other commands. Does anybody have an idea what causes the problem?

Upvotes: 2

Views: 1927

Answers (3)

Charles Stewart
Charles Stewart

Reputation: 11837

When bash is invoked using sh, it starts up in a special, POSIX-compliant mode. This has different syntax, which I guess explains the different results.

See bashref of POSIX mode, #22: "process substitution is not available".

Upvotes: 1

soulmerge
soulmerge

Reputation: 75724

That syntax doesn't look familiar. Are you sure you are using bash in your terminal? You can verify by typing echo $SHELL.

Upvotes: 0

codaddict
codaddict

Reputation: 455152

Try

bash test.sh

or

chmod ugo+x test.sh
./test.sh

Works fine for me when I do either.

Looks like the syntax is not supported by the bourne shell (sh).

Upvotes: 5

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