awk(1)

awk [opt] program [input]
+    -F <sepstr>        field separator string (can be regex)
+    program            awk program
+    input              file or stdin if not file given
+

Input processing

Input is processed in two stages:

Splitting input into a sequence of records. +By default split at newline character, but can be changed via the +builtin RS variable.
Splitting a record into fields. By default strings without whitespace, +but can be changed via the builtin variable FS or command line option +-F.

Fields are accessed as follows:

$0 whole record
$1 field one
$2 field two
...

Program

An awk program is composed of pairs of the form:

pattern { action }
+

The program is run against each record in the input stream. If a pattern +matches a record the corresponding action is executed and can access the +fields.

INPUT
+  |
+  v
+record ----> ∀ pattern matched
+  |                   |
+  v                   v
+fields ----> run associated action
+

Any valid awk expr can be a pattern.

Special pattern

awk provides two special patterns, BEGIN and END, which can be used +multiple times. Actions with those patterns are executed exactly once.

BEGIN actions are run before processing the first record
END actions are run after processing the last record

Special variables

RS record separator: first char is the record separator, by default +
FS field separator: regex to split records into fields, by default +
NR number record: number of current record

Special statements & functions

+
printf "fmt", args...
+
Print format string, args are comma separated.
+
- %s string
- %d decimal
- %x hex
- %f float
+
Width can be specified as %Ns, this reserves N chars for a string. +For floats one can use %N.Mf, N is the total number including . and +M.
+
+
strftime("fmt")
+
Print time stamp formatted by fmt.
+
- %Y full year (eg 2020)
- %m month (01-12)
- %d day (01-31)
- %F alias for %Y-%m-%d
- %H hour (00-23)
- %M minute (00-59)
- %S second (00-59)
- %T alias for %H:%M:%S
+

Examples

Filter records

awk 'NR%2 == 0 { print $0 }' <file>
+

The pattern NR%2 == 0 matches every second record and the action { print $0 } +prints the whole record.

Capture in variables

# /proc/<pid>/status
+#   Name:    cat
+#   ...
+#   VmRSS:   516 kB
+#   ...
+
+for f in /proc/*/status; do
+    cat $f | awk '
+             /^VmRSS/ { rss = $2/1024 }
+             /^Name/ { name = $2 }
+             END { printf "%16s %6d MB\n", name, rss }';
+done | sort -k2 -n
+

We capture values from VmRSS and Name into variables and print them at the +END once processing all records is done.

Run shell command and capture output

cat /proc/1/status | awk '
+                     /^Pid/ {
+                        "ps --no-header -o user " $2 | getline user;
+                         print user
+                     }'
+

We build a ps command line and capture the first line of the processes output +in the user variable and then print it.

+ +

fish(1)

Quick Info

Fish initialization file ~/.config/fish/config.fish

Switch between different key bindings:

fish_default_key_bindings to use default key bindings
fish_vi_key_bindings to use vi key bindings

Variables

Available scopes

local variable local to a block
global variable global to shell instance
universal variable universal to all shell instances + preserved across +shell restart

Set/Unset Variables

set <name> [<values>]
+    -l  local scope
+    -g  global scope
+    -U  universal scope
+    -e  erase variable
+    -S  show verbose info
+    -x  export to ENV
+    -u  unexport from ENV
+

Lists

In fish all variables are lists (start with index 1, but lists can't +contain lists.

set foo a b c d
+
+echo $foo[1]      # a
+echo $foo[-1]     # d
+echo $foo[2..3]   # b c
+echo $foo[1 3]    # a c
+

$ can be seen as dereference operator.

set foo a; set a 1337
+echo $$foo  # outputs 1337
+

Cartesian product.

echo file.{h,cc}
+# file.h file.cc
+
+echo {a,b}{1,2}
+# a1 b1 b2
+

Special Variables (Lists)

$status      # exit code of last command
+$pipestatus  # list of exit codes of pipe chain
+
+$CMD_DURATION   # runtime of last command in ms
+

`*PATH`

Lists ending with PATH are automatically split at : when used and joined +with : when exported to the environment.

set -x BLA_PATH a:b:c:d
+echo $BLA_PATH              # a b c d
+env | grep BLA_PATH         # BLA_PATH=a:b:c:d
+

Command Handling

# sub-commands are not run in quotes
+echo "ls output: "(ls)
+

I/O redirection

# 'noclobber', fail if 'log' already exists
+echo foo >? log
+

Control Flow

`if` / `else`

if grep foo bar
+    # do sth
+else if grep foobar bar
+    # do sth else
+else
+    # do sth else
+end
+

`switch`

switch (echo foo)
+case 'foo*'
+    # do start with foo
+case bar dudel
+    # do bar and dudel
+case '*'
+    # do else
+end
+

`while` Loop

while true
+    echo foo
+end
+

`for` Loop

for f in (ls)
+    echo $f
+end
+

Functions

Function arguments are passed via $argv list.

function fn_foo
+    echo $argv
+end
+

Autoloading

When running a command fish attempts to autoload a function. The shell looks +for <cmd>.fish in the locations defined by $fish_function_path and loads +the function lazily if found.

This is the preferred way over monolithically defining all functions in a +startup script.

Helper

functions         # list al functions
+functions foo     # describe function 'foo'
+functions -e foo  # erase function 'foo'
+
+funced foo        # edit function 'foo'
+                  # '-e vim' to edit in vim
+

Prompt

The prompt is defined by the output of the fish_prompt function.

function fish_prompt
+    set -l cmd_ret
+    echo "> "(pwd) $cmd_ret" "
+end
+

+
Use set_color to manipulate terminal colors.
+

Useful Builtins

# history
+history search <str>   # search history for <str>
+history merge          # merge histories from fish sessions
+
+# list
+count $var            # count elements in list
+
+# string
+string split SEP STRING
+

Keymaps

  Shift-Tab ........... tab-completion with search
+  Alt-Up / Alt-Down ... search history with token under the cursor
+  Alt-l ............... list content of dir under cursor
+  Alt-p ............... append '2>&1 | less;' to current cmdline
+

Debug

  status print-stack-trace .. prints function stacktrace (can be used in scripts)
+  breakpoint ................ halt script execution and gives shell (C-d | exit
+                              to continue)
+

+ +

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