How to improve generation speed of PS1 in this code? - linux

Question

PROMPT_COMAND runs slow. Code optimization needed.
I use bash builtin PROMPT_COMMAND to customize PS1. Too much echo | grep commands were executed to get colorful git branch indication.The prompt runs much slower. Any ideas about optimazation?
function git_branch {
branch="`git branch 2>/dev/null | grep "^\*" | sed -e "s/^\*\ //"`"
if [ "${branch}" != "" ];then
if [ "${branch}" = "(no branch)" ];then
branch="(`git rev-parse --short HEAD`...)"
fi
echo "$branch"
fi
}
# display last two dentry
function get_curdir {
dir=$(pwd);
last_dirent=${dir##*/}
dir=${dir%/*}
lastbutone_dirent=${dir##*/}
echo -n "${lastbutone_dirent}/${last_dirent}"
}
# colours
RED="\[\033[1;31m\]"
GREEN="\[\033[1;32m\]"
BROWN="\[\033[0;33m\]"
BLUE="\[\033[1;34m\]"
PURPLE="\[\033[1;35m\]"
CYAN="\[\033[1;36m\]"
GRAY="\[\033[0;37m\]"
LIGHT_RED="\[\033[0;31m\]"
LIGHT_GREEN="\[\033[1;32m\]"
LIGHT_BLUE="\[\033[0;34m\]"
YELLOW="\[\033[1;33m\]"
LIGHT_PURPLE="\[\033[1;35m\]"
LIGHT_CYAN="\[\033[1;36m\]"
LIGHT_GRAY="\[\033[0;37m\]"
WHITE="\[\033[1;37m\]"
RESTORE="\[\033[0m\]" #0m restores to the terminal's default colour
function prompt_command {
RET=$?
PS1="${CYAN}[${RESTORE}${GREEN}\u${RESTORE} "
PS1+="${BLUE}$(get_curdir)${RESTORE}${CYAN}]${RESTORE}"
BRANCH=$(git_branch)
if [ "${BRANCH}" != "" ]; then
STATUS="$(git status -s 2>/dev/null)"
if echo "${STATUS}" | grep -e "??"; then
PARENTHESES_COLOR=${RED}
else
PARENTHESES_COLOR=${GREEN}
fi >/dev/null
if [ "${STATUS}" = "" ]; then
BRANCH_COLOR=${GREEN}
else
if echo "${STATUS}" | grep -e "^[ M]M"; then
if echo "${STATUS}" | grep -e "^M[ M]"; then
BRANCH_COLOR=${PURPLE}
else
BRANCH_COLOR=${RED}
fi
elif echo "${STATUS}" | grep -e "^M "; then
BRANCH_COLOR=${YELLOW}
fi
fi >/dev/null
PS1+="${PARENTHESES_COLOR}(${RESTORE}${BRANCH_COLOR}$(git_branch)${RESTORE}${PARENTHESES_COLOR})${RESTORE}"
fi
if [ "$RET" = "0" ]; then
PS1+=" ${CYAN}->${RESTORE} "
else
PS1+=" ${RED}->${RESTORE} "
fi
}
export PROMPT_COMMAND=prompt_command
update
I run a simple test in some dir where a git repo resides and use time to get time cost.
for ((i=0;i<10000;i++));do
prompt_command;
done
Performance of the original version above is:
real 3m4.567s
user 1m32.698s
sys 3m2.495s
Then I change [] to [[ ]], diff like this:
17,18c17,18
< if [ "${branch}" != "" ];then
< if [ "${branch}" = "(no branch)" ];then
---
> if [[ "${branch}" != "" ]];then
> if [[ "${branch}" == "(no branch)" ]];then
58c58
< if [ "${BRANCH}" != "" ]; then
---
> if [[ "${BRANCH}" != "" ]]; then
65c65
< if [ "${STATUS}" = "" ]; then
---
> if [[ "${STATUS}" == "" ]]; then
81c81
< if [ "$RET" = "0" ]; then
---
> if [[ "$RET" == "0" ]]; then
Performance get a little worse
real 3m7.690s
user 1m30.717s
sys 3m6.676s
So, [] doesn't matter.
But builtin regex helps a lot.
When I changes to the following and replace $(pwd) with $PWD
if [ "${BRANCH}" != "" ]; then
regex_untracked=".*^\?\?.*"
regex_staged=".*^M[ M].*"
regex_modified=".*^[ M]M.*"
STATUS="$(git status -s 2>/dev/null)"
if [[ ${STATUS} =~ $regex_untracked ]]; then
PARENTHESES_COLOR=${RED}
else
PARENTHESES_COLOR=${GREEN}
fi >/dev/null
if [[ ${STATUS} =~ $regex_modified ]]; then
if [[ ${STATUS} =~ $regex_staged ]]; then
BRANCH_COLOR=${PURPLE}
else
BRANCH_COLOR=${RED}
fi
elif [[ ${STATUS} =~ $regex_staged ]]; then
BRANCH_COLOR=${YELLOW}
else
BRANCH_COLOR=${GREEN}
fi >/dev/null
PS1+="${PARENTHESES_COLOR}(${RESTORE}${BRANCH_COLOR}$(git_branch)${RESTORE}${PARENTHESES_COLOR})${RESTORE}"
fi
Time consumed decreases:
real 2m15.534s
user 1m1.036s
sys 2m15.043s
By the way, without this colorful branch feature, performance is
real 1m0.478s
user 0m29.499s
sys 1m1.411s

Answer 1

bash has its own built-in regular expression matching. For example, replace
echo "${STATUS}" | grep -e "^[ M]M"
with
regex="^[ M]M"
[[ $STATUS =~ $regex ]]