Redirector "<<<" in Ubuntu?

Question

I'm getting this error

Syntax error: redirection unexpected

in the line:

 if grep -q "^127.0.0." <<< "$RESULT"

How I can run this in Ubuntu?

Code goes from left to right. Been a while, but if I remember correct it is `>> "$RESULT"` to redirect it. — , Apr 16 '13 at 19:15
What do you want to achieve with that command? What is the value of `$RESULT`? — Ansgar Wiechers, Apr 16 '13 at 19:16
@Ansgar - Understood, but the OP appeared to be asking about redirection. — Dave Newman, Apr 16 '13 at 19:19
You should escape the dots "^127\.0\.0\." Otherwise you match strings like "127X0Y0Z" — James, Jun 24 '14 at 13:35
Related: https://stackoverflow.com/questions/7950268/what-does-the-bash-operator-i-e-triple-less-than-sign-mean — Ciro Santilli OurBigBook.com, Jul 24 '23 at 08:10

score 35 · Answer 1 · edited Jul 24 '23 at 07:27

35

<<< is a bash-specific redirection operator (so it's not specific to Ubuntu). The documentation refers to it as a "Here String", a variant of the "Here Document".

3.6.7 Here Strings

A variant of here documents, the format is:

<<< word

The word is expanded and supplied to the command on its standard input.

A simple example:

$ cat <<< hello
hello

If you're getting an error, it's likely that you're executing the command using a shell other than bash. If you have #!/bin/sh at the top of your script, try changing it to #!/bin/bash.

If you try to use it with /bin/sh, it probably assumes the << refers to a "here document", and then sees an unexpected < after that, resulting in the "Syntax error: redirection unexpected" message that you're seeing.

zsh and ksh also support the <<< syntax.

edited Jul 24 '23 at 07:27

Ciro Santilli OurBigBook.com

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answered Apr 16 '13 at 19:34

Keith Thompson

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ksh supports it. dash doesn’t. – Josh Lee Apr 16 '13 at 19:37
Would it be accurate to say it's a shorthand for `cat <(echo "hello")`? (I'm just asking to deepen my understanding) – Sridhar Sarnobat Oct 17 '17 at 19:26
7

@Sridhar-Sarnobat: Not quite. `cat <<< hello` invokes `cat` with no arguments, with stdin redirected from a temporary file containing `hello` followed by a newline. `cat <(echo hello)` invokes `cat` with a single argument, which is the name of a pseudo-file from which it can read the same data. `cat` behaves similarly with no arguments and stdin redirected vs. with a single argument naming a file to be read, but other commands can behave differently. For example, on my system `ls -l /proc/self/fd/0 << – Keith Thompson Oct 17 '17 at 22:59

score 25 · Accepted Answer · answered Apr 16 '13 at 19:41

25

if grep -q "^127.0.0." <<< "$RESULT"
then
    echo IF-THEN
fi

is a Bash-specific thing. If you are using a different bourne-compatable shell, try:

if echo "$RESULT" | grep -q "^127.0.0."
then
    echo IF-THEN
fi

answered Apr 16 '13 at 19:41

Hal Canary

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score 2 · Answer 3 · answered Apr 16 '13 at 19:16

2

It works for me on Ubuntu, if I complete you IF block:

if grep -q "^127.0.0." <<< "$RESULT"; then echo ""; fi

answered Apr 16 '13 at 19:16

Jakuje

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What does <<< do? This may be something new to me. – Dave Newman Apr 16 '13 at 19:18
http://stackoverflow.com/questions/2462317/bash-syntax-error-redirection-unexpected – jmginer Apr 16 '13 at 19:19
@Ansgar Thanks! Learned something new today. – Dave Newman Apr 16 '13 at 19:20
not run in Ubuntu: http://stackoverflow.com/questions/2462317/bash-syntax-error-redirection-unexpected – jmginer Apr 16 '13 at 19:26
Not Ubuntu problem, but it doesn't run in dash. in bash works fine (since I have in Ubuntu default bash). – Jakuje Apr 16 '13 at 19:29

Redirector "<<<" in Ubuntu?

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