Home » Differences between sed on Mac OSX and other “standard” sed?

Differences between sed on Mac OSX and other “standard” sed?


OS X currently comes with a FreeBSD sed from 2005. Most of the differences below also apply to other BSD sed versions.

OS X’s sed uses -E for ERE and GNU sed uses -r. -E is an alias for -r in GNU sed (added in 4.2, not documented until 4.3). Newer versions of FreeBSD and NetBSD sed support both -E and -r. OpenBSD sed only supports -E.

-i '' works with OS X’s sed but not GNU sed. -i works with GNU sed, recent versions of NetBSD, OpenBSD sed, but not OS X’s sed. -i -e works with both but in the case of FreeBSD sed makes a backup of the original file with -e appended to the file name (and you need to pass no more than one expression to sed).

GNU sed interprets escape sequences like t, n, 01, x01, w, and b. OS X’s sed and POSIX sed only interpret n (but not in the replacement part of s).

GNU sed interprets |, +, and ? in BRE but OS X’s sed and POSIX sed don’t. (, ), {, and } are POSIX BRE.

GNU sed allows omitting ; or a newline before } but OS X’s sed doesn’t.

i (insert), a (append), and c (change) have to be followed by a backslash and a newline in OS X’s sed and POSIX sed but not in GNU sed. GNU sed adds a missing newline after the text inserted by i, a, or c but OS X’s sed doesn’t. For example sed 1ia is a GNU alternative to sed $'1i\nan'.

For example printf a|sed -n p adds a newline in OS X’s sed but not in GNU sed.

OS X’s sed doesn’t support the I (case-insensitive) or M (multi-line) modifiers. Newer versions of FreeBSD sed support I.

OS X’s sed doesn’t support -s (--separate), -u (--unbuffered), or -z (--null-data).

One BSD option that is not supported by GNU sed is -a, which makes w append to a file instead of truncating a file.

Examples of GNU sed commands that don’t work with OS X’s sed:

sed /pattern/,+2d # like `sed '/pattern/{N;N;d;}'`
sed -n 0~3p # like `awk NR%3==0`
sed /pattern/Q # like `awk '/pattern/{exit}1'` or `sed -n '/pattern/,$!p'`
sed 's/b./u&/g' # u converts the next character to uppercase
sed 's/^./l&/' # l converts the next character to lowercase
sed -i '1ecat file_to_prepend' file # e executes a shell command
sed -n l0 # 0 disables wrapping

The behavior of shell utilities does differ in minor ways between unix variants. There are many unix variants, with a complex history. There are standardisation efforts such as the POSIX standard and its superset the Single UNIX specification. Most systems nowadays implement POSIX:2001, also known as the Single UNIX Specification version 3, with minor deviations and many extensions. The Single Unix specification is not a tutorial, but version 3 is readable if you already have an idea of what a command is doing. You can consult it to know if some feature is standard or an extension of a particular system.

A majority of unix users use Linux and haven’t used any other variant. Linux comes with GNU utilities, which often have many extensions to the standard. So you’ll find quite a lot of code out there that works on Linux but not on other unices, because it relies on those extensions.

Regarding sed, consult the sed Single Unix specification for the minimum that every system is supposed to support, the man page on your system for what your implementation supports, and the GNU sed manual for what most people out there use.

One of the nonstandard extensions in GNU sed is supporting multiple commands run together. For example, this GNU sed program prints all lines containing an a, but changes b into c first:

sed -ne '/a/ {s/b/c/g; p}'

{ and } are actually separate commands, so for full portability, you need to specify them either on separate lines (in a file) or in separate -e arguments (on the command line). The lack of a command separator after { and the use of ; as a command separator are common extensions. The lack of a command separator before } is a less common extension. This is standard-compliant:

sed -n -e '/a/ {' -e 's/b/c/g' -e p -e '}'

This is nonstandard but commonly accepted:

sed -ne '/a/ { s/b/c/g; p; }'

Another nonstandard but common extension is the use of n to mean a newline in a s replacement text (the use in a regexp is standard). The portable method is to include backslash-newline in the sed script. Another common extension is +, ? and | in regexps to mean one or more, at most one and alternation; portable basic regular expressions have none of these. For example, the first command is a non-portable way of replacing contiguous sequences of whitespace by a newline; the second command is a standards-compliant equivalent.

sed -e 's/ +/n/'
sed -e 's/  */

The best way I have found to have the same script work on both Linux and Mac is to:

sed -i.bak -e 's/foo/bar/' -- "${TARGET}" &&
  rm -- "${TARGET}.bak"

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...