title  sh/bash/ksh reference.
author GPL(C) Mohsin Ahmed, http://www.cs.albany.edu/~mosh
vim:ft=sh:

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section Quick_sh_ksh_bash
moshtag=shell,ksh,sh,case,for,select,until,esac

    case word in [ ( pattern [ | pattern ] ... ) list ;; ] ... esac
    select name [ in word ] ; do list ; done
    for name [ in word ] ; do list ; done
    if list; then list; [ elif list; then list; ] ... [ else list;  ]
    while list; do list; done
    until list; do list; done
    [ function ] name () { list; }

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moshtag=FD,file_descriptors,dup
moshtag=>,>>,<,<<,>&,<&,<&-,>&-,<>

File Descriptors in Bourne shell.

        F is filename,
        &F is filehandle.

        fd 0 stdin, '-'.
        fd 1 stdout
        fd 2 stderr

> F    Redirect stdout to file F.
E> F    Redirect fd E to file F.
        Only param and command subst,
        Not filename or blank interpretations.
            Eg. $ >b cat a .. copies a to b.
            Eg. $ echo x > *.c  .. creates '*.c'

E<>F   Redirect E to file F in read-write mode

E>&D    fd D is duped and result is fd E (default is stdout).
        stderr to stdout, dup fd1 into fd2.


E<&D    fd D is duped and result is fd E (default is stdin).

<&-    close stdin
>&-    close stdout
E<&-    close fd E (default is stdin /0).
E>&-    close fd E (default is stdout/1).

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Shell ReDirection Examples:                 moshtag=redirection

Order of redirection is always left to right.
    Eg. $ gcc x.c       2>&1 | grep errors

    Eg. $ gcc x.c > log 2>&1
        1. First send stdout 1> to ./log
        2. Then  send stderr 2> to &1 (ie. ./log)

    Eg. $ exec 5>./config.log ; echo "into config.log" 1>&5

    Eg. $ cmd 3>&1 1>&2 2>&3 3>&-   # Swap stdout and stderr for cmd
        1. First save stdout as &3.
        2. Next send stdout to stderr
        3. Send stderr to &3 (stdout)
        4. close &3

    Eg. stderr_output=`cmd 3>&1 1>&2 2>&3 3>&-`

----------- --------------------------------------
Redirection Meaning
----------- --------------------------------------
0</dev/null Make STDIN give immediate EOF
1>/dev/null Discard STDOUT
2>/dev/null Discard STDERR
2>&1        Send STDERR to STDOUT instead
2>&-        Close STDERR (not recommended)
3<>/dev/tty Open fd 3 to /dev/tty in read-write mode
----------- --------------------------------------

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PatternMatch: One SquareParen and Two Equals.    moshtag=[
eg. 

if [ "${FILE}" == "./*" && -r "${FILE}" ] ;then 
    echo "$PWD/$FILE readable" 
fi
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Expr: (see man expr).                           moshtag=expr

$(expr string : 're') .. string =~ m/^re/ .. returns strlen of match.
                      .. string =~ m/re\(re\)re/ .. \1 is returned, else 0.
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$(substr string from len)
$(index  string substr)
$(length string)

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                                            moshtag=expr-regexp

eg. A=`expr $A + 1`
    expr 'src-mosh.c' : '.*-\(.*\)\.c' .. returns 'mosh'.
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                                            moshtag=toupper,lolower,uc,lc
Uppercasing var value:
    word=$(echo $word | tr [a-z] [A-Z])
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                                                moshtag=base_n
ksh base convertor (base 2..36 ok):
    typeset -i16 x=30  ;echo $x    # prints 16#1e, x in hex/base 16.
    typeset -i2 x=12#20  ;echo $x # prints x (12#20=24) in binary 2#11000.

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                                            moshtag=yesterday_tz
Get date two days ago: TZ=GMT+48 date

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                                               moshtag=subst
Variable Subst:
    ${VAR/pat/str}
    ${VAR//pat/str}
    ${VAR/#pat/str}
    ${VAR/%pat/str}
    $((ArithExpr))
    $[ArithExpr]

DIR="${PWD//[\/:]/_}" # Convert :/ to _.
P="${PWD//\//_}"; Q="${P//:/_}";  .. c:/mohsin/perl -> c__mohsin_perl
Local file to url: F="file://$(hostname)/${F/:/}"
Eg. echo "${X//\//\\}"  .. $X =~ s,/,\\,g; .. slash to backslashes.

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                                                     moshtag=##,%%

Variables:
    % %% Remove tail, eg. TTY=${TTY%/dev/ttyp} ie.  /dev/ttyp0 => /dev/ttyp
    # ## Remove head, eg. TTY=${TTY#/dev/ttyp} ie.  /dev/ttyp0 => 0
Examples:
    BASENAME=${FILE%%.*}
    EXTENSION=${FILE##*.}
    for i in *.c ; do
        if [[ ! -r "${i%%.*}.o" ]] ; then  # file.c => file.o
            gcc $i
        fi
    done
    ${VAR:offset:len}
    ${VAR:offset}
 
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                                        moshtag=lasterror,$?

cmp -x file1 file2; echo "exit status=$?" # lasterror $?
: "${1:?'Need Arg1'}"
: "${X:?}"  .. check X is set.
: ${T:=DefaultT}
: ${X:-Default3rd}
TMP=${$WINDIR+c:/tmp} .. c:/tmp if $WINDIR.

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                                        moshtag=interactive_shell
Interactive shells: Run this as "x.ksh" and ". x.ksh"
    case $- in # ((
    *i*) INTERACTIVE=1;;
    *) INTERACTIVE=0;;
    esac
    if [ "$-" == "*i*" ] ; then echo interactive_shell ; fi
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                                        moshtag=select_ask
Select: .. Example .. IFS,Select menu, default.
ask_diff(){
    TAB='   '
    DIFF_CHOICES="diff -wb${TAB}vim -od${TAB}vim -d${TAB}xdiff\
                ${TAB}ediff${TAB}windiff${TAB}cp -vi${TAB}:"
    OFS=$IFS
    IFS=$TAB
    select diff in $DIFF_CHOICES ; do
        echo diff=${diff:='windiff'}
        break
    done
    IFS=$OFS
}
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                                        moshtag=ediff
ediff(){ ${EMACS:=emacs} --eval "(ediff-files \"$1\" \"$2\")" }

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                                        moshtag=ksh_args,CMDLINEARG,opt.txt

    # ksh tips

    CMD=${0##*/}
    CMD=${0##*\\}
    CMD=${CMD%.*}

    # Evaluate overriding cmdline args.
    #     for i       ; do ; echo $i ; done
    # === for i in $* ; do; echo $i; done

    for CMDLINEARG  # remember $*
    do
        case $CMDLINEARG in
        [A-Z]*=*) echo
            echo "Overriding variable, eval $CMDLINEARG"
            eval "$CMDLINEARG"
            ;;
        -*) echo "
    USAGE: $CMD [OPTIONS] ... Does x y z.
    OPTIONS:
    "
            exit
        esac
    done

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