bash condition test if - ghdrako/doc_snipets GitHub Wiki

Condition

• && and operator
• || or operator

# succeed with the cd or bail with a message
cd $DIR || { echo "cd to $DIR failed." ;  exit ; }
# the && and || operators are of equal precedence and are left Associated
[ -n "$DIR" ] && [ -d "$DIR" ] && cd "$DIR" || exit 2

test

Istnieją dwie wersje test. Jedna jako polecenie wbudowane w powloke i drugie jako samodzielny program. Domyślnie pierwszeństwo mają polecenia wbudowane. Aby wywołać wersję samodzielna trzeba podać ścieżkę.

Polecenie test zawsze zwraca true lub false czyli odpowiednio 0 lub 1. Bez argumentów test zwraca false.

Podstawowa skladnia

test wyrazenie

Aby odwrócić dzialanie

test ! wyrazenie

Połączenie wielu wyrażenie za pomocą opcji -a i -o odpowiednio and i or.

test wyr1 -a wyr2
test wyr1 -o wyr2

Skrócona forma polecenia test to nawiasy kwadratowe

test ! wyrażenie
[! wyrażenie] 

test -f /etc/hosts -a -r /etc/hosts
[ -f /etc/hosts -a -r /etc/hosts ] 
[ -f /etc/hosts -a -r /etc/hosts ] && Cat /etc/hosts

IF structure

[ is a Bash builtin, while [[ is a Bash keyword

[...]

if [ $Name != $USER ]
then
    echo "Your name isn't your username"
else
    echo "Your name is your username"
fi
# True if the value of $Name is not equal to the current user's login username

# NOTE: if $Name is empty, bash sees the above condition as:
if [ != $USER ]
# which is invalid syntax
# so the "safe" way to use potentially empty variables in bash is:
if [ "$Name" != $USER ] ...
# which, when $Name is empty, is seen by bash as:
if [ "" != $USER ] ...
# which works as expected

# There is also conditional execution
echo "Always executed" || echo "Only executed if first command fails"
# => Always executed
echo "Always executed" && echo "Only executed if first command does NOT fail"
# => Always executed
# => Only executed if first command does NOT fail


# To use && and || with if statements, you need multiple pairs of square brackets:
if [ "$Name" == "Steve" ] && [ "$Age" -eq 15 ]
then
    echo "This will run if $Name is Steve AND $Age is 15."
fi

if [ "$Name" == "Daniya" ] || [ "$Name" == "Zach" ]
then
    echo "This will run if $Name is Daniya OR Zach."
fi

[ ... ](/ghdrako/doc_snipets/wiki/-...-)

Nie są kompatybilne z Bourn Shell.

[ ... ](/ghdrako/doc_snipets/wiki/-...-) is more robust than [ ... ] because it handles special characters and logical operators more gracefully. It avoids issues like word splitting and allows for advanced features such as regex-style pattern matching (==, !=). Unlike [ ... ], it does not require special quoting for variables containing spaces.

Jako słowo kluczowe [[ pasuje swoje argumenty zanim powłoka je rozwinie stąd też każdy ponedynczy parametr będzie reprezentowany jako pojedynczy argument.

echo "zawartość pliku" >"moj plik" 
FILE="moj plik" 
[ -f $FILE && -r $FILE ](/ghdrako/doc_snipets/wiki/--f-$FILE-&&--r-$FILE-) && Cat "$FILE" 
[ -f "$FILE" -a -r "$FILE" ] && Cat "$FILE" 

Nie musimy otaczać zmiennych cudzysłowiem ale jest to dobra praktyka. Dodatkowo [[ obsługuje && więc nie trzeba używać -a.

[ ... ](/ghdrako/doc_snipets/wiki/-...-) is specific to Bash and not available in all shells. In POSIX- compliant scripts, [ ... ] should be used.Inside [ ... ](/ghdrako/doc_snipets/wiki/-...-), pattern matching works without needing * to be quoted, whereas [ ... ] requires careful quoting to avoid globbing and expansion.

Dopasowanie wzorca

[ $FILE = *.pl ](/ghdrako/doc_snipets/wiki/-$FILE-=-*.pl-) && cp "$FILE" /scripts

Wyrażenia regularne

To samo o powyzej

[ $FILE =~ \.pl$ ](/ghdrako/doc_snipets/wiki/-$FILE-=~-\.pl$-) && cp "$FILE" /scripts

Kropka ma znaczenie w wyrażeniu regularnym została poprzedzone \ aby je dezaktywowac

# There is also the `=~` operator, which tests a string against a Regex pattern:
[email protected]
if [ "$Email" =~ [a-z]+@[a-z]{2,}\.(com](/ghdrako/doc_snipets/wiki/net|org)-)
then
    echo "Valid email!"
fi
# Note that =~ only works within double [ ](/ghdrako/doc_snipets/wiki/-) square brackets,
# which are subtly different from single [ ].
# See http://www.gnu.org/software/bash/manual/bashref.html#Conditional-Constructs for more on this.

shopt -s nocasematch # wyłączenie rozróżnianie wielkości liter w wrażeniach regularnych

shopt -u nocasematch # wlaczenie

# Numeric Conditions
[ NUM -eq NUM ](/ghdrako/doc_snipets/wiki/-NUM--eq-NUM-) Equal
[ NUM -ne NUM ](/ghdrako/doc_snipets/wiki/-NUM--ne-NUM-) Not equal
[ NUM -lt NUM ](/ghdrako/doc_snipets/wiki/-NUM--lt-NUM-) Less than
[ NUM -le NUM ](/ghdrako/doc_snipets/wiki/-NUM--le-NUM-) Less than or equal to
[ NUM -gt NUM ](/ghdrako/doc_snipets/wiki/-NUM--gt-NUM-) [ NUM -ge NUM ](/ghdrako/doc_snipets/wiki/-NUM--ge-NUM-) Greater than or equal to

# String Conditions
[ STRING == STRING ](/ghdrako/doc_snipets/wiki/-STRING-==-STRING-) # Equal
[ STRING != STRING ](/ghdrako/doc_snipets/wiki/-STRING-!=-STRING-) # Not Equal
[ -z STRING ](/ghdrako/doc_snipets/wiki/--z-STRING-)        # Empty string
[ -n STRING ](/ghdrako/doc_snipets/wiki/--n-STRING-)        # Not empty string
[ STRING =~ STRING ](/ghdrako/doc_snipets/wiki/-STRING-=~-STRING-) # Regular expression match

# check string pattern matching
input="hello123"
if [ $input == hello* ](/ghdrako/doc_snipets/wiki/-$input-==-hello*-); then
echo "The input starts with 'hello'"
else
echo "The input does not start with 'hello'"
fi

number=10
if [ $number -gt 5 && $number -lt 20 ](/ghdrako/doc_snipets/wiki/-$number--gt-5-&&-$number--lt-20-); then
echo "The number is between 5 and 20"
fi

# Is the length of the variable zero? i.e., empty or null
if [ -z "$VAR" ](/ghdrako/doc_snipets/wiki/--z-"$VAR"-); then
echo empty
fi

# This checks for a nonzero length, i.e., not empty, not null
if [ -n "$VAR" ](/ghdrako/doc_snipets/wiki/--n-"$VAR"-); then
echo "VAR has a value:" $VAR
fi
# Same here
if [ "$VAR" ](/ghdrako/doc_snipets/wiki/-"$VAR"-); then
echo even easier this way
fi

#File Conditions
[ -f FILE ](/ghdrako/doc_snipets/wiki/--f-FILE-) # Is a file
[ -d FILE ](/ghdrako/doc_snipets/wiki/--d-FILE-) # Is a directory
[ -e FILE ](/ghdrako/doc_snipets/wiki/--e-FILE-) # Exists
[ -r -w -x FILE ](/ghdrako/doc_snipets/wiki/--r--w--x-FILE-) # Is readable, Writable, executable
[ -h FILE ](/ghdrako/doc_snipets/wiki/--h-FILE-) # Is symbolic link

#File Conditions Example
if [ ! -f ./pdfgen/pdfgen ]; then
    echo "Building pdfgen binary"
    npm run --prefix pdfgen build:linux
else
    echo "Pdfgen binary already exists, skipping build"
fi


if [ ! -L /usr/local/bin/heroku ];
then
    wget https://cli-assets.heroku.com/branches/stable/heroku-linux-amd64.tar.gz
    sudo mkdir -p /usr/local/lib /usr/local/bin
    sudo tar -xvzf heroku-linux-amd64.tar.gz -C /usr/local/lib
    sudo ln -s /usr/local/lib/heroku/bin/heroku /usr/local/bin/heroku
fi

# Boolean conditions:
a|[ ! EXPR ](/ghdrako/doc_snipets/wiki/-!-EXPR-) |Not
a|[ BOOL && BOOL ](/ghdrako/doc_snipets/wiki/-BOOL-&&-BOOL-) |And
a|[ BOOL ](/ghdrako/doc_snipets/wiki/|-BOOL-) |OR

the double bracket syntax supports an additional comparison operator, =~, which allows the use of regular expressions.

if [ $FN =~ .*xyzz*.*jpg ](/ghdrako/doc_snipets/wiki/-$FN-=~-.*xyzz*.*jpg-); then ...

Check if an environment variable is set in bash

# long
if [ -z "${CIRCLE_BRANCH}" ](/ghdrako/doc_snipets/wiki/--z-"${CIRCLE_BRANCH}"-); then
    npm run redis-cli flushall
fi
 
npm run sync

# one-liner
[-z "${CIRCLE_BRANCH}"] && npm run redis-cli flushall; npm run sync

Przypisanie wartości domyslnej

name=$1
[ -z $name ] && name="Anonymous" 

prosciej

name={$1-"Anonymous"}