Zsh Primer for Busy People

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Zsh
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CLI
2017-07-11 · 3 min read

Check zshall for comprehensive description of Zsh features. Here's a Zsh guide.

Zsh has five data types: integer, float, scalar (a string), array and hash. Types are handled automatically with the exception of hashes which requires to declare a variable as a hash table using built-in typeset -A <variable name>.

typeset -Z 3 makes a variable at least three characters long padded with zeros if necessary.

typeset -Z 3 name
name=7
print $name

007

typeset -r make a variable readonly.

typeset -r name
name=Bond

 zsh: read-only variable: name

typeset -U create a unique set out of a list

typeset -U unique_set
unique_set=(1 1 1 2 2 3 3 1 2 3 3 5 4 4 4 5)
print $unique_set

1 2 3 5 4
  • !! -> the previous command
  • !str -> the most recent command starting with str
  • !?str[?] -> the most recent command containing str

Quickies

Extract command's part

echo This is a very long command with many options and arguments
!:4-5

very long command

Replace command's part 1

echo This is a very long command with many options and arguments
!!:s/echo/cat

cat This is a very long command with many options and arguments

Replace command's part 2

less file.txt
^less^vim
vim file.txt

Check if variable exists

(( $+var )) && print “\tvar exists”
(( $+var )) || print “\tno, it doesn’t exist”

Convert GIFs to JPGs

for i in **/*.gif; convert $i $i:r.jpg

Convert PDFs to PNGs

for i in *.pdf; sips -s format png --rotate 270 --resampleHeight 1140 $i --out $i:r.png

Check the entire filesystem to see if any executable files have been modified since yesterday

print -l /**/*(*.m-1)

Remove spaces in the file name

for i in *.pdf; mv $i $i:gs/\ //

Create files with range

touch file-99{01..05}.tmp

Array

Assign content of /usr/bin to list

list=(/usr/bin/*)

In zsh, arrays are indexed from 1 (instead of 0). Use a $# before the array name to get its size.

print $#list

Modifiers

Read about Zsh modifiers at man zshexpn.

Flags

str="hello, world!"
print -l ${(U)str} ${str:u} $str

HELLO, WORLD
HELLO, WORLD
hello, world

Files

Find files that changed today

ls *(m0)

Find Rakefile anywhere under current directory

ls **/Rakefile

List files bigger that 64mb

ls **/*(Lm+20)

List transformation

list=(
  /usr/bin/perl
  /var/log/wtmp
  /etc/inetd.conf
)

-t -> similar to basename, it removes all leading pathname components, leaving the tail

print ${list:t}
perl wtmp inent.conf

-h -> similar to dirname, it removes a trailing pathname component, leaving the head

print ${list:h}
/usr/bin /var/log /etc

Text search through elements of list, similar to grep

print ${(M)list:#/etc*}
/etc/inted.conf

Inverted grep:

print ${list:#/etc*}
/usr/bin/perl /var/log/wtmp

Combine modifiers

list=(/usr/bin/*)
print -l ${${(UM)list:#*ssh*}:t}

SSH
SSH-ADD
SSH-AGENT
SSH-KEYGEN
SSH-KEYSCAN

Arrays can have both positive and negative numbers used as indexes. Positive numbers count forward from the start of the array; negative numbers count backward from the end of the array.

Retrieve sub-list

print $list[10,17]

Hash

Declare a hash and assign key-value pairs to it

typeset -A hash
hash=(key value alice macos bob win10 jenny freebsd)
print $hash

win10 freebsd value macos
print $hash[jenny]

freebsd

Add new element

hash[mike]=winxp
print $hash

win10 winxp freebsd value macos

Remove element

unset hash[mike]

Scripting

Bourne shell scripts are usually difficult to write in a portable way, because they often rely on external programs to do data transformation, zsh on the other hand has the capabilities of many traditional Unix programs built into it. In order to keep Zsh scripts as portable as possible you should always use its built-in features.

ZMV

zmv moves (or renames) files based on the pattern. Its manual is in the zshcontrib man page. zmv must be loaded with autoload zmv to be available.

Use -n to perform a dry run with zmv.

zmv '* *' '$f:gs/ /_’
zmv '*.(*).(*).([0-9][0-9])*.mkv' '$1_$2-$3.mkv'
i=0; zmv -n '*' 'file_${(l:3::0:)$((++i))}'

mv -- '2013-04-28 15.55.50.jpg' file_001
mv -- '2013-11-20 10.56.35.jpg' file_002
mv -- '2014-04-23 11.14.18.jpg' file_003