123 lines
3.9 KiB
Markdown
123 lines
3.9 KiB
Markdown
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# Bash scripting basics
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Kommt immer zu begin eines neuen Scripts
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```
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#!/bin/bash
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```
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Berechtigung um ausgeführt zu werden
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```
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chmod +x FILENAME
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```
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## Description Numeric Comparison String Comparison
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```
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Shell comparison example: [ 100 -eq 50 ]; echo $? [ "GNU" = "UNIX" ]; echo $?
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less than -lt <
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greater than -gt >
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equal -eq =
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not equal -ne !=
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less or equal -le N/A
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greater or equal -ge N/A
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boolean
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true=0
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false=1
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```
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```
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Operator Description
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! EXPRESSION The EXPRESSION is false.
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-n STRING The length of STRING is greater than zero.
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-z STRING The lengh of STRING is zero (ie it is empty).
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[ -a FILE ] True if FILE exists.
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[ -b FILE ] True if FILE exists and is a block-special file.
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[ -c FILE ] True if FILE exists and is a character-special file.
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[ -d FILE ] True if FILE exists and is a directory.
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[ -e FILE ] True if FILE exists.
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[ -f FILE ] True if FILE exists and is a regular file.
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[ -g FILE ] True if FILE exists and its SGID bit is set.
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[ -h FILE ] True if FILE exists and is a symbolic link.
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[ -k FILE ] True if FILE exists and its sticky bit is set.
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[ -p FILE ] True if FILE exists and is a named pipe (FIFO).
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[ -r FILE ] True if FILE exists and is readable.
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[ -s FILE ] True if FILE exists and has a size greater than zero.
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[ -t FD ] True if file descriptor FD is open and refers to a terminal.
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[ -u FILE ] True if FILE exists and its SUID (set user ID) bit is set.
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[ -w FILE ] True if FILE exists and is writable.
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[ -x FILE ] True if FILE exists and is executable.
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[ -O FILE ] True if FILE exists and is owned by the effective user ID.
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[ -G FILE ] True if FILE exists and is owned by the effective group ID.
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[ -L FILE ] True if FILE exists and is a symbolic link.
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[ -N FILE ] True if FILE exists and has been modified since it was last read.
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[ -S FILE ] True if FILE exists and is a socket.
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STRING1 = STRING2 STRING1 is equal to STRING2
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STRING1 != STRING2 STRING1 is not equal to STRING2
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INTEGER1 -eq INTEGER2 INTEGER1 is numerically equal to INTEGER2
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INTEGER1 -gt INTEGER2 INTEGER1 is numerically greater than INTEGER2
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INTEGER1 -lt INTEGER2 INTEGER1 is numerically less than INTEGER2
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```
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## Example if then else in bash
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```
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#!/bin/bash
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num_a=400
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num_b=200
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if [ $num_a -lt $num_b ]; then
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echo "$num_a is less than $num_b!"
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else
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echo "$num_a is greater than $num_b!"
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fi
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```
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## IF ELSE && CASE
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```
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if Perform a set of commands if a test is true.
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else If the test is not true then perform a different set of commands.
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elif If the previous test returned false then try this one.
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&& Perform the and operation.
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|| Perform the or operation.
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case Choose a set of commands to execute depending on a string matching a particular pattern.
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fi End of if
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```
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## Variabeln
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```
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name='Someone' -Nur Text kann man in einem String speichern.
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username=$(whoami) -funktionen werden mit $() angegeben
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day=$(date +%A) -parameter können ohne Probleme in die Klammer schreiben.
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```
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## Command Exec
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der befehl kommt ohne syntax einfach auf eine leere zeile z.b.
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```
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fortune
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cowsay hallo
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```
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ich kann die beiden commands aber auch zusammensetzen
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```
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fortune | cowsay
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```
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## stderr stdout
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The difference between stdout and stderr output is an essential concept as it allows us to a threat, that is, to redirect each output separately. The > notation is used to redirect stdout to a file whereas 2> notation is used to redirect stderr and &> is used to redirect both stdout and stderr. The cat command is used to display a content of any given file
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