How to capture stderr of a bash keyword (e.g. time)?

Question

I want to time reading bash history and put the result into a variable. Unfortunately, time (which is a shell keyword) prints the result to stderr, and apparently redirecting stderr from shell keywords doesn't work the same as redirecting regular command output. In other words,

foo=$(time history -r 2>&1)

doesn't work (foo variable is empty, output is printed to terminal). How can I capture the output of time keyword?

Note: since history is a shell builtin, I cannot use external time command (i.e. /usr/bin/time) - I have to use time keyword in bash.

http://mywiki.wooledge.org/BashFAQ/032 – m0dular Mar 13 '18 at 21:37 — m0dular, Mar 13 '18 at 21:37

score 4 · Accepted Answer · answered Mar 11 '18 at 11:31

4

You can use the following syntax:

foo=$((time history -r) 2>&1)

Placing the command in a () and redirect its stderr to stdout

Example:

$ foo=$((time history -r) 2>&1)
$ echo $foo
real 0m0.001s user 0m0.000s sys 0m0.000s
$

answered Mar 11 '18 at 11:31

Yaron

4,289

1

or with just { time history -r; } instead of ( ), it doesn't need a subshell in particular – ilkkachu Mar 11 '18 at 11:41

How to capture stderr of a bash keyword (e.g. time)?

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