1 © 2001 John Urrutia. All rights reserved. Chapter 13 The Z shell and Advanced Shell Programming.

1© 2001 John Urrutia. All rights reserved.

Chapter 13

The Z shell and Advanced Shell Programming


TopicsBackground

Variables

The Builtins

Command Processing

Shell Programs

Z Shell Options


Z Background iz deesDeveloped from the Korn Shell found

primarily on System V UNIX systems.

Combines many features of bash, tcsh, and ksh

Extensive help (man zshall or man zsh)

Strong script programming features


Startup FilesThe Four System startup files set

systemwide global defaults/etc/zshenv – Always executes first &

only once when zsh starts.

/etc/zprofile – runs at login startupNot executed if –f option is usedUsed to modify environment to mimic bash or

ksh


Startup Files/etc/zshrc – sets interactive defaults

Not executed if –f option is usedExecuted only when stdin and stdout are

connected.

/etc/zlogin – sets login defaultsUsed to modify environment to mimic C or

tcsh


Startup FilesThe Four user startup files override

systemwide defaults.zshenv – overrides /etc/zshenv variables

Not executed if –f option is used2nd file to execute when zsh starts.

.zprofile – overrides /etc/profile variablesNot executed if –f option is usedUsed to modify environment to mimic bash or

ksh


Startup Files.zshrc – overrides /etc/zshrc variables

Not executed if –f option is usedExecuted only when stdin and stdout are

connected.

.zlogin – overrides /etc/zlogin variablesUsed to modify environment to mimic C or

tcsh


TopicsBackground

Variables

The Builtins

Command Processing

Shell Programs

Z Shell Options


VariablesDeclared as in bash – no whitespace

Variablename=Value

If whitespace is needed it must be enclosed in quotation marks

Referenced by preceding $${…} are required if variable is followed

by a letter, digit or underscore.


VariablesCommand line argument reference

$0 Command

$1 … $9 first nine arguments

${10 … } for all other arguments

Deleting variablesunset – will remove variable values and

attributes.


VariablesVariable Attributes

Use the typeset built-in to set attributes-l set variable to lowercase-u set variable to uppercase-i set variable to integer-x export variable

By default all variables are stringsArithmetic functions against strings causes

Conversion to integer Manipulation Conversion back to string



typeset -i or integer designate numerics

integers by default are considered to be base 10 numbers but can be set to any other base.typeset -i 2 BINARY

Sets the base to 2


Variableslinux1% numvar=65261

linux1% typeset –i 16 hexnum

linux1% hexnum=$numvar

linux1% echo $numvar $hexnum

65261 16#FEED



typeset -x or exportCauses the variables to be copied and made available to any child processes

When applied to a function all sub-shells can execute the function.


VariablesVariable Attributes - Formatting

Causes the variables to be justified and padded with spaces to a width of number typeset -L number (justify left pad right)typeset -R number (justify right pad left)

Causes the variables to be justified right and padded with zeroes to a width of number typeset -Z number (justify left pad right)


VariablesVariable Attributes - readonly

Marks variables as unchangeable .typeset -r or readonly

Values must be set before marking.

Attributes can be viewed bytypeset variable nameDOES NOT WORK ANYMORE!


Variable LocalityBy default all variables are global

Recognized throughout the current shell and all sub-shells.

Local variablesDefined and recognized only within a

function.typeset name


Keyword VariablesThree categories

ModifiableSet and used by environment

ReadonlySet and used by environment

SpecialPerform special functions


Keyword VariablesSpecial variables

# - number of command line arguments

* - all command line arguments together

@ - all command line arguments separate

_ - previous commands last line argument


Keyword VariablesEnvironment variables

LINENO – Line number of script where referenced

PPID – PID of parent proccess

LINES – lines on display (default 24) COLUMNS– columns on display (default 80) PS3 – bash equivalent


Keyword VariablesEnvironment variables

PS4 – Trace IDUsed by the debugging facilitySet by set -x

RANDOM – each reference sets to 0-32767

SECONDS– # of sec’s since shell started

TMOUT – # of sec’s until logout


Controlling the PromptDefault for zsh - $HOSTNAME%

Common options for PS1%~ – Pathname of working directory

%. – Working directory tail ( no pathname)

%m or M – hostname - with DOMAIN

%n – $USERNAME variable

%W – date in format mm/dd/yy


Controlling the PromptNot so Common option for PS1

%n (x . true-text . False-text )n – represents the number to comapre to.

(zero by default)

. – represents a separation character (or /)

x – represents the test character.true-text - text to display if test is true.false-text - text to display if test is false.


Controlling the PromptPS1=`%(?/True:/False:)`

Test Charactersw – if day of week = n (0 – Sunday)d – if day of month = nD – if month = n (0 – January)? – last exit status was 0

Text can include additional %(x .true-text.False-text )


Expanding Shell VariablesVariables can be expanded using

prefix and suffix control characters# - Remove minimal matching prefixes

## - Remove maximal matching prefixes

% - Remove minimal matching suffixes

%% - Remove maximal matching suffixes


Expanding Shell Variableslinux1% somefile=/home/usr/name.c

linux1% echo ${somefile#/*/}

usr/name.c

linux1% echo ${somefile##/*/}

name.c

linux1% echo ${somefile%/*}

/home/usr

linux1% echo ${somefile%%/*}

linux1%


Array Variablesz shell supports single dimensional

arraysvarname=(value1 value2 value3 …)

Entire array is referenced by $varname

Array element(s) is/are referenced by

$varname [n ] – one element

$varname [n,x ] – range of elements


Array Variables Non-integer subscripts

$varname [@] – creates a duplicate array each element is exactly the sameNewArray=“$OldArray[@]”

$varname [*] – splits array into charactersNewArray=“$OldArray[*]”

Does not work …


Array Variables by the byte

…% OldArray=(this old man)

…% NewArray=“$OldArray[*]”

…% echo ${#NewArray}

12

…% echo $NewArray[4,-4]

s old


Arithmeticlet – builtin

…% let “NewVar=OldVar*10+NewVar”No spaces, must be quoted to prevent shell

expansion.You can assign multiple variables on a line

…% ((NewVar=OldVar*10+NewVar))Shortcut method – NO QUOTES NEEDED

…% echo $((2*NewVar))

…% echo $((2*$NewVar))

These are the same…

However


Arithmeticlet – builtin with arrays

…% days_in_month=(31 28 31 30 …)

…% echo $((days_in_month[2]))0 This refers to the variable days_in_month[2]

This refers to the array days_in_month[2]…% echo $(($days_in_month[2]))

28

Not anymore!


Math, Logic & Relational Operators

MathUnary

+, -, ++, --, <<, >>

Binary*, /, %, **, +, -


Math, Logic & Relational Operators

LogicBinary (bitwise comparison)

&, ^, |

Relational<, >, <=, >=, ==, !=

&&, ^^, ||


TopicsBackground

Variables

The Builtins

Command Processing

Shell Programs

Z Shell Options


The BuiltinsControl Structures

if…then

for…in

while

case

until

repeat

Select

Like bash

Like bash

Like bash

Use either

test (expression)

Or

[[expression]]


Basic Syntax for Structuresselect varname in arguments

do•••

done


getoptsGet Options

Sets the valid list of option characters

If option takes an argument it is stored in OPTARG

The : indicates the option requires an argument

while getopts :bt:u arg


getopts in useProblem: Write a script that can take

3 options.-b ignore whitespace at start of line

-u translate all output to uppercase

-t [arg] use the directory provided


getoptsSKIPBLANKS=TMPDIR=\tmpCASE=lowerwhile getopts bt:u argdocase $arg in b) SKIPBLANKS=TRUE ;; t) if [[ -d “$OPTARG” ]]

thenTMPDIR=$OPTARG

elseprint “$0: -t takes directory argument.” >&2exit 1

fi;; u) CASE=upper ;;esac


Input and Outputread [-qEA] [-un] [varname…]

Reads input from the filestream and places it into one or more variables

-q query reads 1 char. if ‘y’ or ‘Y’ set variable to ‘y’ otherwise set it to ‘n’

-E echoes the typed words after the return key

-A breaks input into words based on IFS


Input and Outputread [-qEA] [-un] [varname…]

-un use the specified filestream forinput.

Read will prompt the user for input using the following formatread varname\?”Enter something”

Read sets exit status 0 if successful & set a 1 at eof.


Input and Outputprint [-ncoO] [-un] [string to

print…]-n supress newlines

-c display output in columns

-o sort arguments ascending (-O decending)

The string to print can contain escape characters for formatting


File DescriptorsAdditional files can be opened for use by

using the “exec” builtinexec 3> outputfile

exec 6< inputfile

File descriptors can be duplicated using redirection operatorsa <& v

Files can be closed exec 3<&-


What does this function do?mycp(){ case $# in 0) exec 3<&0 4<&1 ;; 1) exec 3< $1 4<&1 ;; 2) exec 3< $1 4> $2 ;; *) print “Usage: mycp [source [dest]]”

exit 1;; esac cat <&3 >&4 exec 3<&- 4<&-}


FunctionsDeclared the same as in bash

function func_name{Commands}

func_name(){Commands}


Functionsbreak – will terminate a function.

unfunction – will delete a function.

autoload – load when executed.


TopicsBackground

Variables

The Builtins

Command Processing

Shell Programs

Z Shell Options


Command ProcessingBasically follows the same process as

bash.Token splitting

History substitution

Alias substitution

Filename Expansion

Command substitution

Parameter expansion

Etc.


Command ProcessingProcess Substitution

Substitutes filenames with processes

<(command ) - output of command is directed to a named pipe (FIFO) which is substituted for the input file

>(command ) - output is directed to a named pipe (FIFO) which is substituted for standard input to command


I/O Redirection & the Coprocess

Allows the creation of a parallel process that runs in the background and communicates directly with the parent shell.

Connected with a 2-way pipe<&p – read the standard output

>&p – write to standard input


I/O Redirection & the Coprocess

Create coprocess

Beginparallel

execution

Parent shell

print…>&p

read…<&p

Read stdin

Write stdout

Co-process


TopicsBackground

Variables

The Builtins

Command Processing

Shell Programs

Z Shell Options


RecursionDoing yourself

Recursion is the execution of the function within the function.

Dependency on the completion of the previous iteration.


makepathMakepath()

{ if [[ ${#1} –eq 0 || -d “$1” ]] then

return 0 fi if [[ “${1%/*}” = “$1” ]]

then mkdir $1 return $?

fi makepath ${1%/*} || return 1 mkdir $1 return $?

}

1 © 2001 John Urrutia. All rights reserved. Chapter 13 The Z shell and Advanced Shell Programming.

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Transcript of 1 © 2001 John Urrutia. All rights reserved. Chapter 13 The Z shell and Advanced Shell Programming.