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ssledz/bash-cheat-sheet

Created May 21, 2016 14:36
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  1. JasWSInc created this gist Jul 17, 2014.
    285 changes: 285 additions & 0 deletions bash-cheat-sheet
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    B A S H C H E A T S H E E T

    to page output forward (only): command filename | more
    to page output forward & back: command filename | less
    to print a dataset: lp datasetname (-d printerid) (-o landscape)

    USE OF QUOTATION MARKS
    echo "$varname" = echo The value of \$varname is \"$varname\"
    = echo "The value of \$varname is \"$varname\"."
    $fred='Four spaces between these words.'
    echo $fred yields Four spaces between these words.
    echo "$fred" yields Four spaces between these words.

    SPECIAL CHARACTERS
    ~ home directory # comment
    $ variable expression & background job
    ; shell command separator / pathname directory separator
    \ quote (escape) next character | pipe
    * string wildcard ? single-character wildcard
    ( start subshell ) end subshell
    [ start character-set wildcard ] end character-set wildcard
    { start command block } end command block
    ' strong quote (prevents subs) " weak quote (allows subs)
    < input redirect > output redirect
    ! logical NOT || logical OR
    && logical AND \ Return continue on next line
    . (dot builtin: execute) : (null builtin: returns true)
    << here document >> append output

    FILE ATTRIBUTE OPERATORS
    -e file exists example: if [ ! -e filename ]; then
    echo "filename does not exist"
    else ....
    fi
    -d file exists and is a directory
    -f file exists and is a normal file
    -r user has read permission for the file
    -s file exists and is not empty
    -w user has write permission for the file
    -x user has execution permission for a normal file, or
    user has search permission for a directory
    -O user owns the file
    -G user's group id has access to the file
    -nt newer than (modification date-time of file
    -ot older than for file-to-file comparison)

    ARITHMETIC ASSIGNMENT
    let x=1+4 value of $x is 5
    ='1 + 4' 5
    ='(2+3) * 5' 25
    ='2 + 3 * 5' 17
    ='17 / 3' 5
    ='17 % 3' 2
    bitwise:
    ='1<<4' 16 00001 -> 10000
    ='48>>3' 6 110000 -> 000110
    ='17 & 3' 1 10001 & 11 -> 00001
    ='17 | 3' 19 10001 | 11 -> 10011
    ='17 ^ 3' 18 10001 ^ 11 -> 10010

    I/O REDIRECTORS
    cmd1 | cmd2 use stdout of cmd1 as stdin for cmd2
    > file save stdout to file
    < file use file as stdin
    >> file append stdout to file (create file if nonexistent)
    >| file force stdout to file (even if noclobber is set)
    n>| file force stdout to file from descriptor n (even...)
    <> file use file as both stdin and stdout (process in place)
    n<> file use as both stdin and stdout for file descriptor n
    << label use here-document (within scripts specifies batch input)
    n> file direct file descriptor n to file
    n< file take file descriptor n from file
    n>> file append descriptor n to file (or create file for n)
    n>& duplicate stdout to file descriptor n
    n<& duplicate stdin from file descriptor n
    n>&m make file descriptor n a copy of the stdout fd
    n<&m make file descriptor n a copy of the stdin fd
    >&file send stdout and stderror to file
    <&- close stdin
    >&- close stdout
    n<&- close input from file descriptor n
    n>&- close output from file descriptor n

    STRING COMPARISON OPERATORS INTEGER COMPARISON OPERATORS
    (truth = 0) (truth = 1)
    = matches -lt less than
    != does not match -le less than or equal
    < less than -eq equal
    > greater than -ge greater than or equal
    -n not null (length > 0) -gt greater than
    -z null (length = 0) -ne not equal
    ARITHMETIC OPERATORS RELATIONAL OPERATORS
    + addition < less than
    - subtraction > greater than
    * multiplication <= less than or equal to
    / division (w/ truncation) >= greater than or equal to
    % remainder == equal to
    << bit-shift left != not equal to
    >> bit-shift right && logical and
    & bit-wise and || logical or
    | bit-wise or
    ~ bit-wise not
    ! bit-wise not
    ^ bit-wise exclusive or

    ARITHMETIC EXPRESSION: $(( ))
    echo "Only $(( (365-$(date +%j)) / 7 )) weeks until the New Year"

    KEYWORD VARIABLES
    BASH_ENV startup file path INPUTRC readline start default
    CDPATH 'cd' searchpath LANG locale default
    COLUMNS width of display LC_* locale categories
    FCEDIT default fc editor LINES height of display
    HISTFILE history list path MAIL mail pathname
    HISTSIZE max hist entries MAILCHECK how often, in seconds
    HOME user default dir MAILPATH :-separated list for mail
    IFS field separators PATH :-separated list for cmds
    and many, many more
    SUBSTITUTION OPERATORS
    ${#varname} returns the length of varname
    ${varname:-word} returns word if varname is undefined
    ${varname:=word} sets varname to word if varname is undefined
    ${varname:+word} returns word if varname exists and isn't null,
    otherwise returns null
    ${varname:?message} prints varname and message
    and aborts command if varname is undefined
    ${varname:offset(:length)
    returns parts of strings beginning at offset
    for the specified length (default s total)
    special circumstance: when varname is "@",
    length means number of positional parameters
    starting at positional parameter offset
    PATTERN MATCHING
    ${variable#pattern} if pattern matches beginning of variable's value
    delete shortest part that matches, return rest
    ${variable##pattern} if pattern matches beginning of variable's value
    delete longest part that matches, return rest
    ${variable%pattern} if pattern matches end of variable's value
    delete shortest part that matches, return rest
    ${variable%%pattern} if pattern matches end of variable's value
    delete longest part that matches, return rest
    ${variable/pattern/string}
    longest match to pattern in variable is
    replaced by string (first match only)
    ${variable//pattern/string}
    longest match to pattern in variable is
    replaced by string (all possible matches)
    for the two latter:
    if pattern begins with #, match must be at beginning
    of variable; if pattern begins with %, match must
    be at end of variable
    if string is null, matches are deleted
    if variable is @ or *, operation is applied to each
    positional parameter in turn
    for variable Path with value /home/me/book/long.file.name :
    ${Path##/*/} long.file.name
    ${Path#/*/} me/book/long.file.name
    $Path /home/me/book/long.file.name
    ${Path%.*} /home/me/book/long.file
    ${Path%%.*} /home/me/book/long

    CONTROL KEY USAGE ('stty -a' gives complete list)
    Cntl-C cancel current comand (first try)
    Cntl-\ cancel current command (second try)
    Cntl-L clear the screen
    Cntl-D end of input
    Cntl-? erase last character
    Cntl-W erase last word
    Cntl-U erase entire command line
    Cntl-O flush
    Cntl-S halt output to screen
    Cntl-V next line
    Cntl-R reprint
    Cntl-Y restart current command
    Cntl-Q restart output to screen
    Cntl-M return
    Cntl-Z suspend current command



    PROMPT STRINGS
    PS1 primary prompt string default "\s-\v\$"
    PS2 secondary prompt string default ">"
    PS3 selection menu p.s. default "#?"
    PS4 debug prompt string default "+" per level of expansion

    PROMPT STRING CUSTOMIZATIONS
    \a ASCII bell character (007) \H hostname
    \e ASCII escape key (033) \h hostname up to the first "."
    \d date as Weekday Month Day \T time in 12-hr HH:MM:SS
    \n carriage return, line feed \t time in 24-hr HH:MM:SS
    \s shell name \@ time in HH:MM am/pm
    \u username \v version of bash
    \w working directory \V version, patchlevel of bash
    \W basename of working directory \# command number
    \$ root as #, user as $ \! history number
    \nnn character code in octal \\ backslash
    \[ begin non-printing characters \] end non-printing characters

    FREQUENTLY USED REGULAR EXPRESSIONS
    city, state zip '^.*, [A-Z][A-Z] [0-9]{5}-[0-9]{4} '
    month, day, year '[A-Z][a-z]\{3,9\} [0-9]\{1,2}, [0-9]\{4\}'
    soc-sec-number '[0-9]\{3\}-[0-9]\{2\}-[0-9]\{4\}'
    telephone number '[0-9]\{3\}-[0-9]\{3\}-[0-9]\{4\}'
    dollars and cents '\$ [0-9]*\.[0-9]\{2\}
    blank line '^$'
    an entire line '^.*$'
    one or more spaces ' *'
    for best results, invoke bash with the --posix option

    CONTROL FLOW

    if condition-1 ; then case test-string in
    {statement-block-1} pattern1 ) {statements
    elif condition-2 ; then using $expression} ;;
    {statement-block-2} pattern2 ) {more statements} ;;
    else {statement-block-n} * ) {error processing} ;;
    fi esac

    for loop-index (in list) select name in list;
    do do
    {statements using $name} {statements using $name}
    done done

    while condition until condition
    do do
    {statement-block} {statement-block}
    done done

    default list is $@
    condition for 'while', 'until' checked at top of loop
    'break','continue' valid in 'for', 'while', 'until' lopps




    VARIABLES ALWAYS AVAILABLE WITHIN A SCRIPT
    $0 script name $1 first passed parameter
    $* all parameters but $0 $2 second passed parameter
    $# number of tokens in $* $n nth passed parameter
    $? exit status of a command
    $$ process id
    $@ quoted passed parameters ("$1","$2",...) and all keyword parms

    USER-DEFINED VARIABLES
    assign a value: variable=value echo $variable -> value
    remove a value: variable= echo "$variable" -> value
    remove a variable: unset variable echo '$variable' -> $variable
    use the value: $variable echo \$variable -> $variable
    assign an attribute: declare -attribute variable
    remove an attribute: declare +attribute variable
    attributes include -a array
    -f function
    -i integer
    -r readonly
    -x export
    multiple attributes per variable may occur in a single command

    ORDER OF COMMAND-LINE TRANSFORMATION
    brace expansion
    tilde expansion
    parameter expansion
    variable expansion
    command substitution
    arithmetic expansion
    word-splitting
    filename/pathname expansion
    transformation is triggered by
    & ; / * ? ' " ` [] () $ <> {} ^ # /\ % ~

    '#! /bin/bash' identifies bash as the scripting language
    '#! /bin/sed' identifies sed as the scripting language
    '#! /bin/gawk' identifies gawk as the scripting language
    these must be first characters on first line of the script

    'grep -c string filename' will give a count of occurences of string
    within the file
    'diff oldfile newfile' shows unique oldfile lines with <
    and unique newfile lines with >
    'xxd' will give a hex dump, or reverse it; -E gives ebcdic to the right

    'exit' will collapse a shell; to check for return status > 0,
    execute script from a secondary shell: 'bash scriptname'

    \X'nn ' is marker for hex value of an ASCII character