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The bash shell#

These are programming notes for programming in the bash shell.

---

Redirecting IO#

2>file		send stderr to file

2>&1		send stderr to stdout

---

Accessing shell arguments#

$0	command name

$1	first argument

$@	all arguments

$#	number of arguments

shift	shift arguments

---

List iteration#

(In this example, through all the arguments)

for var in $@; do
    echo $var
done

---

Variable assignment#

var=val      no space around =

---

for loops#

for ((i=1 ; i < 5 ; i++)); do
    echo $i
done

---

Arrays#

Start from 0

a[3]=val	assignment

${a[3]}		get value

a=(val1 val2 val3)	make array

${#a[@]}	number of elements

${a[@]}		all elements as a list

---

Conditionals#

if [ condition ]; then
   ....
elif [ condition ]; then
   ....
else
   ....
fi

---

Conditions#

-f file		if file exists
-d dir		if dir exists
a = b		string equal
a != b		string not equal
-z x		string is null
x		string is not null
x -eq y		x numerically equal to y
x -ne y		x numerically not equal to y
x -gt y		x gretar than y
x -lt y		x less than y
x -ge y		x gretar than or equal to y
x -le y		x less than or equal to y
! cond		not condition

if [ cond ] &&  [ cond ]; then
   ...
fi
if [ cond ] ||  [ cond ]; then
   ...
fi

---

here documents - inline input#

cmd << label
..
..
..
label

all lines up to label are input into command