Bash bugs

Bugs or inconsistencies between Bash versions discovered along making this library.

You can test the examples with the script bash.sh in the repository that runs docker with a specific Bash version. You can pass the script to it by using here document with a quoted delimiter, so not to care about quotes.

$ ./bash.sh 4.2 -x <<'EOF'
The script to test.
EOF

Bash<4.3 preserves quotes in `${var//repl/<here>}`¶

a='}}'; echo "${a//'}}'/'}'}"

Bash	output
<=4.3	`'}'`
>=4.4	`}`

Bash<4.4 declare -p outputs quoted arrays and $'\001' in front of $'\001' and $'\177' bytes.¶

a=(); declare -p a

Bash	output
<=4.3	`declare -a a='()'`
>=4.4	`declare -a a=()`

a=$'\001\177'; printf "%q\n" "$(declare -p a)"

Bash	output
<=4.3	`$'declare -- a="\001\001\001\177"'`
>=4.4	`$'declare -- a="\001\177"'`

Bash>=4.0 all hell breaks loose with IFS=$'\001'¶

Bash greater or equal version 4.0. Tested up to version 5.3-rc2.

IFS=$'\001'; a=(one); printf "%q " "${a[@]}"

Bash	output
>=4.0	`'' '' o '' n '' e`
3.2	`one`

I recommend using ASCII group separator character L_GS=$'\035' for a custom separator.

Bash==3.1 [[ =~ is incompatible with 3.2 because quoting change¶

The problem is that the argument to =~ after Bash3.2 doesn't have to be quoted.

This makes porting scripts to Bash 3.1 painful.

[[ a =~ (a) ]]; echo $?

Bash	result
>=3.2	`0`
<=3.1	`syntax error near (a`

Bash==4.2.53 segfaults when using array variable inside (( )) and using it again after comma operator.¶

a=(1); (( b = a[0], a = b ))

Bash	result
==4.2	segmentation fault, exit code 139
!=4.2

Bash<=4.2 wrongly evaluates arrays in (( )) when array is used twice¶

array=1; (( array[0]<0 ? tmp=array[0] : (tmp=2) )); echo "tmp=$tmp"

Bash	output
<=3.1	`tmp=2`
>=3.2,<=4.1	`tmp=1`
>=4.2	`tmp=2`

Calling a function with a lot of arguments is slow¶

When optimizing L_argparse I noticed a particular slowdown - the function was really short, but still profiling showed it is very slow. Turns out the act of calling the function with a lot of arguments is very slow.

Refactoring to using a global array brought significant speedup.

Bash>=4.2<=5.1 removes empty elements from an array after # array expansion¶

arr=(hhh); arr=("${arr[@]#hhh}"); echo "${#arr[@]}"

Bash	output
<=4.1	1
>=4.2,<=5.1	0
>=5.2	1

Bash==4.1 removes empty elements from an array after /# array expansion¶

arr=(hhh); arr=("${arr[@]/#hhh}"); echo "${#arr[@]}"

Bash	output
==4.2	0
!=4.2	1