In both bash and zsh, there are multiple methods to check whether a command exists. In this post, a set of speed tests will be performed on them to find the fastest way in each of the two shells (NOT to compare the two shells). We will test 5 different methods ( foobar is the command to test for existence in the list):

type foobar &> /dev/null

hash foobar &> /dev/null

command -v foobar &> /dev/null

which foobar &> /dev/null

(( $+commands[foobar] )) (zsh only)

All the methods listed above will have a return status of zero if the command foobar exists, otherwise non-zero. That is, after replacing testing-command by any of the commands listed above, you can test the existence of the command foobar by executing testing-command && echo exist || echo non-exist .

Throughout this post, ls will be the command that is used for testing existence, which does exist on the system which runs the tests. The test environment is Debian Jessie with bash 4.3.30 and zsh 5.0.7 on Intel Xeon processor E3-1240 v3 (8 MB Cache, 3.4 GHz). The test scripts are also available at the end of the post.

Bash

The testing results for bash is shown in the following table, with each testing command running for 100,000 times:

Testing Command Running Time (real, user, sys) type ls &>/dev/null 0m1.476s, 0m0.632s, 0m0.836s hash ls &>/dev/null 0m1.598s, 0m0.740s, 0m0.856s command -v ls &>/dev/null 0m1.441s, 0m0.660s, 0m0.776s which ls &>/dev/null 2m0.418s, 0m3.852s, 0m13.212s

According to the results, type and command -v are the two fastest ways to test the existence of a command in bash. I have also run the tests with either set +h or set -h , but the results do not have obvious difference.

Zsh

The testing results for bash is shown in the following table, with each testing command running for 2,000,000 times:

Testing Command Running Time (real, user, sys) type ls &>/dev/null 0m8.29s, 0m3.48s, 0m4.80s hash ls &>/dev/null 0m5.92s, 0m2.49s, 0m3.42s command -v ls &>/dev/null 0m8.85s, 0m3.61s, 0m5.18s which ls &>/dev/null 0m8.24s, 0m3.18s, 0m5.00s (( $+commands[ls] )) 0m4.01s, 0m3.99s, 0m0.00s

According to the results, (( $+commands[ls] )) is a clear winner in zsh.

(Note that the which command in zsh is significantly faster than in bash, since the which command is a builtin command in zsh but an external command in bash.)

Test Scripts

The test script for bash:

#!/bin/bash N=100000 cmd=ls echo echo "type:" time(for i in $(eval echo "{1..$N}"); do type $cmd &>/dev/null done) echo echo "hash:" time(for i in $(eval echo "{1..$N}"); do hash $cmd &>/dev/null done) echo echo "command -v:" time(for i in $(eval echo "{1..$N}"); do command -v $cmd &>/dev/null done) echo echo "which:" time(for i in $(eval echo "{1..$N}"); do which $cmd &>/dev/null done)

The test script for zsh: