Home » Why is “echo” so much faster than “touch”?

Why is “echo” so much faster than “touch”?


In bash, touch is an external binary, but echo is a shell builtin:

$ type echo
echo is a shell builtin
$ type touch
touch is /usr/bin/touch

Since touch is an external binary, and you invoke touch once per file, the shell must create 300,000 instances of touch, which takes a long time.

echo, however, is a shell builtin, and the execution of shell builtins does not require forking at all. Instead, the current shell does all of the operations and no external processes are created; this is the reason why it is so much faster.

Here are two profiles of the shell’s operations. You can see that a lot of time is spent cloning new processes when using touch. Using /bin/echo instead of the shell builtin should show a much more comparable result.

Using touch

$ strace -c -- bash -c 'for file in a{1..10000}; do touch "$file"; done'
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 56.20    0.030925           2     20000     10000 wait4
 38.12    0.020972           2     10000           clone
  4.67    0.002569           0     80006           rt_sigprocmask
  0.71    0.000388           0     20008           rt_sigaction
  0.27    0.000150           0     10000           rt_sigreturn

Using echo

$ strace -c -- bash -c 'for file in b{1..10000}; do echo >> "$file"; done'
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 34.32    0.000685           0     50000           fcntl
 22.14    0.000442           0     10000           write
 19.59    0.000391           0     10011           open
 14.58    0.000291           0     20000           dup2
  8.37    0.000167           0     20013           close

As others have answered, using echo will be faster than touch as echo is a command which is commonly (though not required to be) built-in to the shell. Using it dispenses with the kernel overhead associated with running starting a new process for each file that you get with touch.

However, note that the fastest way to achieve this effect is still to use touch, but rather than running the program once for each file, it is possible to use the -exec option with find to ensure that is only run a few times. This approach will usually be faster since it avoids the overhead associated with a shell loop:

find . -name "*.xml" -exec touch {} +

Using the + (as opposed to ;) with find ... -exec runs the command only once if possible with each file as an argument. If the argument list is very long (as is the case with 300,000 files) multiple runs will be made with an argument list which has a length close to the limit (ARG_MAX on most systems).

Another advantage to this approach is that it behaves robustly with filenames containing all whitespace characters which is not the case with the original loop.

echo is a shell builtin. On the other hand, touch is an external binary.

$ type echo
echo is a shell builtin
$ type touch
touch is hashed (/usr/bin/touch)

Shell builtins are much faster as there is no overhead involved in loading the program, i.e. there is no fork/exec involved. As such, you’d observe a significant time difference when executing a builtin vs an external command a large number of times.

This is the reason that utilities like time are available as shell builtins.

You can get the complete list of shell builtins by saying:

enable -p

As mentioned above, using the utility as opposed to the builtin results in a significant performance degradation. Following are the statistics of the time taken to create ~9000 files using the builtin echo and the utility echo:

# Using builtin
$ time bash -c 'for i in {1000..9999}; do echo > $i; done'

real    0m0.283s
user    0m0.100s
sys 0m0.184s

# Using utility /bin/echo
$ time bash -c 'for i in {1000..9999}; do /bin/echo > $i; done'

real    0m8.683s
user    0m0.360s
sys 0m1.428s

Related Solutions

Joining bash arguments into single string with spaces

[*] I believe that this does what you want. It will put all the arguments in one string, separated by spaces, with single quotes around all: str="'$*'" $* produces all the scripts arguments separated by the first character of $IFS which, by default, is a space....

AddTransient, AddScoped and AddSingleton Services Differences

TL;DR Transient objects are always different; a new instance is provided to every controller and every service. Scoped objects are the same within a request, but different across different requests. Singleton objects are the same for every object and every...

How to download package not install it with apt-get command?

Use --download-only: sudo apt-get install --download-only pppoe This will download pppoe and any dependencies you need, and place them in /var/cache/apt/archives. That way a subsequent apt-get install pppoe will be able to complete without any extra downloads....

What defines the maximum size for a command single argument?

Answers Definitely not a bug. The parameter which defines the maximum size for one argument is MAX_ARG_STRLEN. There is no documentation for this parameter other than the comments in binfmts.h: /* * These are the maximum length and maximum number of strings...

Bulk rename, change prefix

I'd say the simplest it to just use the rename command which is common on many Linux distributions. There are two common versions of this command so check its man page to find which one you have: ## rename from Perl (common in Debian systems -- Ubuntu, Mint,...

Output from ls has newlines but displays on a single line. Why?

When you pipe the output, ls acts differently. This fact is hidden away in the info documentation: If standard output is a terminal, the output is in columns (sorted vertically) and control characters are output as question marks; otherwise, the output is...

mv: Move file only if destination does not exist

mv -vn file1 file2. This command will do what you want. You can skip -v if you want. -v makes it verbose - mv will tell you that it moved file if it moves it(useful, since there is possibility that file will not be moved) -n moves only if file2 does not exist....

Is it possible to store and query JSON in SQLite?

SQLite 3.9 introduced a new extension (JSON1) that allows you to easily work with JSON data . Also, it introduced support for indexes on expressions, which (in my understanding) should allow you to define indexes on your JSON data as well. PostgreSQL has some...

Combining tail && journalctl

You could use: journalctl -u service-name -f -f, --follow Show only the most recent journal entries, and continuously print new entries as they are appended to the journal. Here I've added "service-name" to distinguish this answer from others; you substitute...

how can shellshock be exploited over SSH?

One example where this can be exploited is on servers with an authorized_keys forced command. When adding an entry to ~/.ssh/authorized_keys, you can prefix the line with command="foo" to force foo to be run any time that ssh public key is used. With this...

Why doesn’t the tilde (~) expand inside double quotes?

The reason, because inside double quotes, tilde ~ has no special meaning, it's treated as literal. POSIX defines Double-Quotes as: Enclosing characters in double-quotes ( "" ) shall preserve the literal value of all characters within the double-quotes, with the...

What is GNU Info for?

GNU Info was designed to offer documentation that was comprehensive, hyperlinked, and possible to output to multiple formats. Man pages were available, and they were great at providing printed output. However, they were designed such that each man page had a...

Set systemd service to execute after fstab mount

a CIFS network location is mounted via /etc/fstab to /mnt/ on boot-up. No, it is not. Get this right, and the rest falls into place naturally. The mount is handled by a (generated) systemd mount unit that will be named something like mnt-wibble.mount. You can...

Merge two video clips into one, placing them next to each other

To be honest, using the accepted answer resulted in a lot of dropped frames for me. However, using the hstack filter_complex produced perfectly fluid output: ffmpeg -i left.mp4 -i right.mp4 -filter_complex hstack output.mp4 ffmpeg -i input1.mp4 -i input2.mp4...

How portable are /dev/stdin, /dev/stdout and /dev/stderr?

It's been available on Linux back into its prehistory. It is not POSIX, although many actual shells (including AT&T ksh and bash) will simulate it if it's not present in the OS; note that this simulation only works at the shell level (i.e. redirection or...

How can I increase the number of inodes in an ext4 filesystem?

It seems that you have a lot more files than normal expectation. I don't know whether there is a solution to change the inode table size dynamically. I'm afraid that you need to back-up your data, and create new filesystem, and restore your data. To create new...

Why doesn’t cp have a progress bar like wget?

The tradition in unix tools is to display messages only if something goes wrong. I think this is both for design and practical reasons. The design is intended to make it obvious when something goes wrong: you get an error message, and it's not drowned in...