# Bash Golf Part 1 > Published at 2021-11-29T14:06:14+00:00; Updated at 2022-01-05 This is the first blog post about my Bash Golf series. This series is about random Bash tips, tricks and weirdnesses I came across. It's a collection of smaller articles I wrote in an older (in German language) blog, which I translated and refreshed with some new content. [2021-11-29 Bash Golf Part 1 (You are currently reading this)](./2021-11-29-bash-golf-part-1.md) [2022-01-01 Bash Golf Part 2](./2022-01-01-bash-golf-part-2.md) [2023-12-10 Bash Golf Part 3](./2023-12-10-bash-golf-part-3.md) [2025-09-14 Bash Golf Part 4](./2025-09-14-bash-golf-part-4.md) ``` '\ . . |>18>> \ . ' . | O>> . 'o | \ . | /\ . | / / .' | jgs^^^^^^^`^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Art by Joan Stark ``` ## Table of Contents * [⇢ Bash Golf Part 1](#bash-golf-part-1) * [⇢ ⇢ TCP/IP networking](#tcpip-networking) * [⇢ ⇢ Process substitution](#process-substitution) * [⇢ ⇢ Grouping](#grouping) * [⇢ ⇢ Expansions](#expansions) * [⇢ ⇢ - aka stdin and stdout placeholder](#--aka-stdin-and-stdout-placeholder) * [⇢ ⇢ Alternative argument passing](#alternative-argument-passing) * [⇢ ⇢ : aka the null command](#-aka-the-null-command) * [⇢ ⇢ (No) floating point support](#no-floating-point-support) ## TCP/IP networking You probably know the Netcat tool, which is a swiss army knife for TCP/IP networking on the command line. But did you know that the Bash natively supports TCP/IP networking? Have a look here how that works: ``` ❯ cat < /dev/tcp/time.nist.gov/13 59536 21-11-18 08:09:16 00 0 0 153.6 UTC(NIST) * ``` The Bash treats /dev/tcp/HOST/PORT in a special way so that it is actually establishing a TCP connection to HOST:PORT. The example above redirects the TCP output of the time-server to cat and cat is printing it on standard output (stdout). A more sophisticated example is firing up an HTTP request. Let's create a new read-write (rw) file descriptor (fd) 5, redirect the HTTP request string to it, and then read the response back: ``` ❯ exec 5<>/dev/tcp/google.de/80 ❯ echo -e "GET / HTTP/1.1\nhost: google.de\n\n" >&5 ❯ cat <&5 | head HTTP/1.1 301 Moved Permanently Location: http://www.google.de/ Content-Type: text/html; charset=UTF-8 Date: Thu, 18 Nov 2021 08:27:18 GMT Expires: Sat, 18 Dec 2021 08:27:18 GMT Cache-Control: public, max-age=2592000 Server: gws Content-Length: 218 X-XSS-Protection: 0 X-Frame-Options: SAMEORIGIN ``` You would assume that this also works with the ZSH, but it doesn't. This is one of the few things which don't work with the ZSH but in the Bash. There might be plugins you could use for ZSH to do something similar, though. ## Process substitution The idea here is, that you can read the output (stdout) of a command from a file descriptor: ``` ❯ uptime # Without process substitution 10:58:03 up 4 days, 22:08, 1 user, load average: 0.16, 0.34, 0.41 ❯ cat <(uptime) # With process substitution 10:58:16 up 4 days, 22:08, 1 user, load average: 0.14, 0.33, 0.41 ❯ stat <(uptime) File: /dev/fd/63 -> pipe:[468130] Size: 64 Blocks: 0 IO Block: 1024 symbolic link Device: 16h/22d Inode: 468137 Links: 1 Access: (0500/lr-x------) Uid: ( 1001/ paul) Gid: ( 1001/ paul) Context: unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 Access: 2021-11-20 10:59:31.482411961 +0000 Modify: 2021-11-20 10:59:31.482411961 +0000 Change: 2021-11-20 10:59:31.482411961 +0000 Birth: - ``` This example doesn't make any sense practically speaking, but it clearly demonstrates how process substitution works. The standard output pipe of "uptime" is redirected to an anonymous file descriptor. That fd then is opened by the "cat" command as a regular file. A useful use case is displaying the differences of two sorted files: ``` ❯ echo a > /tmp/file-a.txt ❯ echo b >> /tmp/file-a.txt ❯ echo c >> /tmp/file-a.txt ❯ echo b > /tmp/file-b.txt ❯ echo a >> /tmp/file-b.txt ❯ echo c >> /tmp/file-b.txt ❯ echo X >> /tmp/file-b.txt ❯ diff -u <(sort /tmp/file-a.txt) <(sort /tmp/file-b.txt) --- /dev/fd/63 2021-11-20 11:05:03.667713554 +0000 +++ /dev/fd/62 2021-11-20 11:05:03.667713554 +0000 @@ -1,3 +1,4 @@ a b c +X ❯ echo X >> /tmp/file-a.txt # Now, both files have the same content again. ❯ diff -u <(sort /tmp/file-a.txt) <(sort /tmp/file-b.txt) ❯ ``` Another example is displaying the differences of two directories: ``` ❯ diff -u <(ls ./dir1/ | sort) <(ls ./dir2/ | sort) ``` More (Bash golfing) examples: ``` ❯ wc -l <(ls /tmp/) /etc/passwd <(env) 24 /dev/fd/63 49 /etc/passwd 24 /dev/fd/62 97 total ❯ ❯ while read foo; do > echo $foo > done < <(echo foo bar baz) foo bar baz ❯ ``` So far, we only used process substitution for stdout redirection. But it also works for stdin. The following two commands result into the same outcome, but the second one is writing the tar data stream to an anonymous file descriptor which is substituted by the "bzip2" command reading the data stream from stdin and compressing it to its own stdout, which then gets redirected to a file: ``` ❯ tar cjf file.tar.bz2 foo ❯ tar cjf >(bzip2 -c > file.tar.bz2) foo ``` Just think a while and see whether you understand fully what is happening here. ## Grouping Command grouping can be quite useful for combining the output of multiple commands: ``` ❯ { ls /tmp; cat /etc/passwd; env; } | wc -l 97 ❯ ( ls /tmp; cat /etc/passwd; env; ) | wc -l 97 ``` But wait, what is the difference between curly braces and normal braces? I assumed that the normal braces create a subprocess whereas the curly ones don't, but I was wrong: ``` ❯ echo $$ 62676 ❯ { echo $$; } 62676 ❯ ( echo $$; ) 62676 ``` One difference is, that the curly braces require you to end the last statement with a semicolon, whereas with the normal braces you can omit the last semicolon: ``` ❯ ( env; ls ) | wc -l 27 ❯ { env; ls } | wc -l > > ^C ``` In case you know more (subtle) differences, please write me an E-Mail and let me know. > Update: A reader sent me an E-Mail and pointed me to the Bash manual page, which explains the difference between () and {} (I should have checked that by myself): ``` (list) list is executed in a subshell environment (see COMMAND EXECUTION ENVIRONMENT below). Variable assignments and builtin commands that affect the shell's environment do not remain in effect after the command completes. The return status is the exit status of list. { list; } list is simply executed in the current shell environment. list must be ter‐ minated with a newline or semicolon. This is known as a group command. The return status is the exit status of list. Note that unlike the metacharac‐ ters ( and ), { and } are reserved words and must occur where a reserved word is permitted to be recognized. Since they do not cause a word break, they must be separated from list by whitespace or another shell metacharacter. ``` So I was right that () is executed in a subprocess. But why does $$ not show a different PID? Also here (as pointed out by the reader) is the answer in the manual page: ``` $ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the subshell. ``` If we want print the subprocess PID, we can use the BASHPID variable: ``` ❯ echo $BASHPID; { echo $BASHPID; }; ( echo $BASHPID; ) 1028465 1028465 1028739 ``` ## Expansions Let's start with simple examples: ``` ❯ echo {0..5} 0 1 2 3 4 5 ❯ for i in {0..5}; do echo $i; done 0 1 2 3 4 5 ``` You can also add leading 0 or expand to any number range: ``` ❯ echo {00..05} 00 01 02 03 04 05 ❯ echo {000..005} 000 001 002 003 004 005 ❯ echo {201..205} 201 202 203 204 205 ``` It also works with letters: ``` ❯ echo {a..e} a b c d e ``` Now it gets interesting. The following takes a list of words and expands it so that all words are quoted: ``` ❯ echo \"{These,words,are,quoted}\" "These" "words" "are" "quoted" ``` Let's also expand to the cross product of two given lists: ``` ❯ echo {one,two}\:{A,B,C} one:A one:B one:C two:A two:B two:C ❯ echo \"{one,two}\:{A,B,C}\" "one:A" "one:B" "one:C" "two:A" "two:B" "two:C" ``` Just because we can: ``` ❯ echo Linux-{one,two,three}\:{A,B,C}-FreeBSD Linux-one:A-FreeBSD Linux-one:B-FreeBSD Linux-one:C-FreeBSD Linux-two:A-FreeBSD Linux-two:B-FreeBSD Linux-two:C-FreeBSD Linux-three:A-FreeBSD Linux-three:B-FreeBSD Linux-three:C-FreeBSD ``` ## - aka stdin and stdout placeholder Some commands and Bash builtins use "-" as a placeholder for stdin and stdout: ``` ❯ echo Hello world Hello world ❯ echo Hello world | cat - Hello world ❯ cat - <