![Conditions
if [expression]; Examples:
then
code if 'expression' is true. #!/bin/bash
if [ "foo" = "foo" ]; then
fi echo “expression
evaluated as true”
fi
#!/bin/bash
if … then T1="foo"
else T2="bar"
if [ "$T1" = "$T2" ]; then
elseif echo “expression
evaluated as true”
else
echo “expression
evaluated as false”
fi](https://image.slidesharecdn.com/scripting101-120531064131-phpapp01/85/Scripting-101-7-320.jpg)
![Loops
3 kinds of loops Examples:
#!/bin/bash
for loop for i in `seq 1 10`; do
echo $i
while loop Done
until loop
#!/bin/bash
COUNTER=0
while [ $COUNTER -lt 10 ]; do
echo “The counter is “ $COUNTER
let COUNTER=COUNTER+1
done](https://image.slidesharecdn.com/scripting101-120531064131-phpapp01/85/Scripting-101-8-320.jpg)
Scripting 101
- 2. My First Sony ^H^H^H hellscript #!/bin/bash echo “Hello World!” $ sh script.sh Hello World
- 3. Output redirection There are 3 file descriptors: Examples: stdin, stdout and stderr. 1. ls -l > ls-l.txt Basically you can: 2. grep da * 2> grep-errors.txt redirect stdout to a file 3. grep da * 1>&2 redirect stderr to a file 4. grep * 2>&1 redirect stdout to a stderr 5. rm -f $(find / -name core) &> /dev/null redirect stderr to a stdout redirect stderr and stdout to a file redirect stderr and stdout to stdout redirect stderr and stdout to stderr 1 'represents' stdout and 2 stderr.
- 4. Pipes Pipes can redirect output from one command to another Example: $ cat /etc/passwd | grep „whoami‟
- 5. Variables STR=“Hello World!” OF=“/var/my-backup-$(date +%Y%m%d).tgz” #!/bin/bash STR=“Hello World!” echo $STR #!/bin/bash OF=“/var/my-backup-$(date +%Y%m%d).tgz” tar -cZf $OF /home/me/
- 6. Local variables #!/bin/bash HELLO=Hello function hello { local HELLO=World echo $HELLO } echo $HELLO hello echo $HELLO
- 7. Conditions if [expression]; Examples: then code if 'expression' is true. #!/bin/bash if [ "foo" = "foo" ]; then fi echo “expression evaluated as true” fi #!/bin/bash if … then T1="foo" else T2="bar" if [ "$T1" = "$T2" ]; then elseif echo “expression evaluated as true” else echo “expression evaluated as false” fi
- 8. Loops 3 kinds of loops Examples: #!/bin/bash for loop for i in `seq 1 10`; do echo $i while loop Done until loop #!/bin/bash COUNTER=0 while [ $COUNTER -lt 10 ]; do echo “The counter is “ $COUNTER let COUNTER=COUNTER+1 done
- 9. Assignment: Write a linux shell script to automagically create 1000 user accounts. Make sure their default password is “Hello123” (hint: you cannot set the pasword with the –p option….)
- 10. Useful files and commands nano, joe, vi (editors) /etc/passwd useradd passwd rm -rf