In a bash script lets take the extreme below examples where the call/start of the myFn() is 5 minutes before the echo of $inVar -> $myvar happens. During this time between the function start and the interaction with the $myvar, it is updated.
myvar=$(... //some json
alpha=hello )
myFn(){
local -n inVar=$1
//wait for 5 mins .... :)
echo $inVar
}
myFn "myvar"
if [ -z $var ]
then
//wait 5 mins
//but life goes on and this is non blocking
//so other parts of the script are running
echo $myvar
fi
myvar=$(... // after 2 mins update alpha
alpha=world
)
As the $myvar is passed to myFn(), when is $myvar actually read,
at myFn call time (when the function is called/starts)
at the reference copy time inVar=$1
when the echo $inVar occurs
and is this the same for other types of processes such as while, if etc?
You're setting inVar as a nameref, so the value is not known until the variable is expanded at the echo statement
HOWEVER
In your scenario, myFn is "non blocking", meaning you launch it in the background. In this case, the subshell gets a copy of the current value of myVar -- if myVar gets updated subsequently, that update is happening in the current shell, not the background shell.
To demonstrate:
$ bash -c '
fn() { local -n y=$1; sleep 2; echo "in background function, y=$y"; }
x=5
fn x &
x=10
wait
'
in background function, y=5
TL;DR: namerefs and background processes don't mix well.
I've been trying to customize my Bash prompt so that it will look like
[feralin#localhost ~]$ _
with colors. I managed to get constant colors (the same colors every time I see the prompt), but I want the username ('feralin') to appear red, instead of green, if the last command had a nonzero exit status. I came up with:
\e[1;33m[$(if [[ $? == 0 ]]; then echo "\e[0;31m"; else echo "\e[0;32m"; fi)\u\e[m#\e[1;34m\h \e[0;35m\W\e[1;33m]$ \e[m
However, from my observations, the $(if ...; fi) seems to be evaluated once, when the .bashrc is run, and the result is substituted forever after. This makes the name always green, even if the last exit code is nonzero (as in, echo $?). Is this what is happening? Or is it simply something else wrong with my prompt? Long question short, how do I get my prompt to use the last exit code?
As you are starting to border on a complex PS1, you might consider using PROMPT_COMMAND. With this, you set it to a function, and it will be run after each command to generate the prompt.
You could try the following in your ~/.bashrc file:
PROMPT_COMMAND=__prompt_command # Function to generate PS1 after CMDs
__prompt_command() {
local EXIT="$?" # This needs to be first
PS1=""
local RCol='\[\e[0m\]'
local Red='\[\e[0;31m\]'
local Gre='\[\e[0;32m\]'
local BYel='\[\e[1;33m\]'
local BBlu='\[\e[1;34m\]'
local Pur='\[\e[0;35m\]'
if [ $EXIT != 0 ]; then
PS1+="${Red}\u${RCol}" # Add red if exit code non 0
else
PS1+="${Gre}\u${RCol}"
fi
PS1+="${RCol}#${BBlu}\h ${Pur}\W${BYel}$ ${RCol}"
}
This should do what it sounds like you want. Take a look a my bashrc's sub file if you want to see all the things I do with my __prompt_command function.
If you don't want to use the prompt command there are two things you need to take into account:
getting the value of $? before anything else. Otherwise it'll be overridden.
escaping all the $'s in the PS1 (so it's not evaluated when you assign it)
Working example using a variable
PS1="\$(VALU="\$?" ; echo \$VALU ; date ; if [ \$VALU == 0 ]; then echo zero; else echo nonzero; fi) "
Working example without a variable
Here the if needs to be the first thing, before any command that would override the $?.
PS1="\$(if [ \$? == 0 ]; then echo zero; else echo nonzero; fi) "
Notice how the \$() is escaped so it's not executed right away, but each time PS1 is used. Also all the uses of \$?.
Compact solution:
PS1='... $(code=${?##0};echo ${code:+[error: ${code}]})'
This approach does not require PROMPT_COMMAND (apparently this can be slower sometimes) and prints [error: <code>] if the exit code is non-zero, and nothing if it's zero:
... > false
... [error: 1]> true
... >
Change the [error: ${code}] part depending on your liking, with ${code} being the non-zero code to print.
Note the use of ' to ensure the inline $() shell gets executed when PS1 is evaluated later, not when the shell is started.
As bonus, you can make it colorful in red by adding \e[01;31m in front and \e[00m after to reset:
PS1='... \e[01;31m$(code=${?##0};echo ${code:+[error: ${code}]})\e[00m'
--
How it works:
it uses bash parameter substitution
first, the ${?##0} will read the exit code $? of the previous command
the ## will remove any 0 pattern from the beginning, effectively making a 0 result an empty var (thanks #blaskovicz for the trick)
we assign this to a temporary code variable as we need to do another substitution, and they can't be nested
the ${code:+REPLACEMENT} will print the REPLACEMENT part only if the variable code is set (non-empty)
this way we can add some text and brackets around it, and reference the variable again inline: [error: ${code}]
I wanted to keep default Debian colors, print the exact code, and only print it on failure:
# Show exit status on failure.
PROMPT_COMMAND=__prompt_command
__prompt_command() {
local curr_exit="$?"
local BRed='\[\e[0;91m\]'
local RCol='\[\e[0m\]'
PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u#\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
if [ "$curr_exit" != 0 ]; then
PS1="[${BRed}$curr_exit${RCol}]$PS1"
fi
}
The following provides a leading green check mark when the exit code is zero and a red cross in all other cases. The remainder is a standard colorized prompt. The printf statements can be modified to present the two states that were originally requested.
PS1='$(if [ $? -eq 0 ]; then printf "\033[01;32m""\xE2\x9C\x93"; else printf "\033[01;31m""\xE2\x9C\x95"; fi) \[\e[00;32m\]\u#\h\[\e[00;30m\]:\[\e[01;33m\]\w\[\e[01;37m\]\$ '
Why didn't I think about that myself? I found this very interesting and added this feature to my 'info-bar' project. Eyes will turn red if the last command failed.
#!/bin/bash
eyes=(O o ∘ ◦ ⍤ ⍥) en=${#eyes[#]} mouth='_'
face () { # gen random face
[[ $error -gt 0 ]] && ecolor=$RED || ecolor=$YLW
if [[ $1 ]]; then printf "${eyes[$[RANDOM%en]]}$mouth${eyes[$[RANDOM%en]]}"
else printf "$ecolor${eyes[$[RANDOM%en]]}$YLW$mouth$ecolor${eyes[$[RANDOM%en]]}$DEF"
fi
}
info () { error=$?
[[ -d .git ]] && { # If in git project folder add git status to info bar output
git_clr=('GIT' $(git -c color.ui=always status -sb)) # Colored output 4 info
git_tst=('GIT' $(git status -sb)) # Simple output 4 test
}
printf -v line "%${COLUMNS}s" # Set border length
date=$(printf "%(%a %d %b %T)T") # Date & time 4 test
test=" O_o $PWD ${git_tst[*]} $date o_O " # Test string
step=$[$COLUMNS-${#test}]; [[ $step -lt 0 ]] && step=0 # Count spaces
line="$GRN${line// /-}$DEF\n" # Create lines
home="$BLD$BLU$PWD$DEF" # Home dir info
date="$DIM$date$DEF" # Colored date & time
#------+-----+-------+--------+-------------+-----+-------+--------+
# Line | O_o |homedir| Spaces | Git status | Date| o_O | Line |
#------+-----+-------+--------+-------------+-----+-------+--------+
printf "$line $(face) $home %${step}s ${git_clr[*]} $date $(face) \n$line" # Final info string
}
PS1='${debian_chroot:+($debian_chroot)}\n$(info)\n$ '
case "$TERM" in xterm*|rxvt*)
PS1="\[\e]0;${debian_chroot:+($debian_chroot)} $(face 1) \w\a\]$PS1";;
esac
Improved demure answer:
I think this is important because the exit status is not always 0 or 1.
if [ $EXIT != 0 ]; then
PS1+="${Red}${EXIT}:\u${RCol}" # Add red if exit code != 0
else
PS1+="${Gre}${EXIT}:\u${RCol}" # Also displays exit status
fi
To preserve the original prompt format (not just colors),
you could append following to the end of file ~/.bashrc:
PS1_ORIG=$PS1 # original primary prompt value
PROMPT_COMMAND=__update_prompt # Function to be re-evaluated after each command is executed
__update_prompt() {
local PREVIOUS_EXIT_CODE="$?"
if [ $PREVIOUS_EXIT_CODE != 0 ]; then
local RedCol='\[\e[0;31m\]'
local ResetCol='\[\e[0m\]'
local replacement="${RedCol}\u${ResetCol}"
# Replace username color
PS1=${PS1_ORIG//]\\u/]$replacement}
## Alternative: keep same colors, append exit code
#PS1="$PS1_ORIG[${RedCol}error=$PREVIOUS_EXIT_CODE${ResetCol}]$ "
else
PS1=$PS1_ORIG
fi
}
See also the comment about the alternative approach that preserves username color and just appends an error code in red to the end of the original prompt format.
You can achieve a similar result to include a colored (non-zero) exit code in a prompt, without using subshells in the prompt nor prompt_command.
You color the exit code portion of the prompt, while having it only appear when non-zero.
Core 2$ section of the prompt: \\[\\033[0;31;4m\\]\${?#0}\\[\\033[0;33m\\]\$ \\[\\033[0m\\]
Key elements:
return code, if not 0: \${?#0} (specificly "removes prefix of 0")
change color without adding to calculated prompt-width: \\[\\033[0;31m\\]
\\[ - begin block
\\033 - treat as 0-width, in readline calculations for cmdline editing
[0;31;4m - escape code, change color, red fg, underline
\\] - end block
Components:
\\[\\033[0;31;4m\\] - set color 0;31m fg red, underline
\${?#0} - display non-zero status (by removing 0 prefix)
\\[\\033[0;33m\\] - set color 0;33m fg yellow
\$ - $ or # on EUID
\\[\\033[0m\\] - reset color
The full PS1 I use (on one host):
declare -x PS1="\\[\\033[0;35m\\]\\h\\[\\033[1;37m\\] \\[\\033[0;37m\\]\\w \\[\\033[0;33m\\]\\[\\033[0;31;4m\\]\${?#0}\\[\\033[0;33m\\]\$ \\[\\033[0m\\]"
Note: this addresses a natural extension to this question, in a more enduring way then a comment.
Bash
function my_prompt {
local retval=$?
local field1='\u#\h'
local field2='\w'
local field3='$([ $SHLVL -gt 1 ] && echo \ shlvl:$SHLVL)$([ \j -gt 0 ] && echo \ jobs:\j)'"$([ ${retval} -ne 0 ] && echo \ exit:$retval)"
local field4='\$'
PS1=$'\n'"\e[0;35m${field1}\e[m \e[0;34m${field2}\e[m\e[0;31m${field3}\e[m"$'\n'"\[\e[0;36m\]${field4}\[\e[m\] "
}
PROMPT_COMMAND="my_prompt; ${PROMPT_COMMAND}"
Zsh
PROMPT=$'\n''%F{magenta}%n#%m%f %F{blue}%~%f%F{red}%(2L. shlvl:%L.)%(1j. jobs:%j.)%(?.. exit:%?)%f'$'\n''%F{cyan}%(!.#.$)%f '
Images of prompt
for ( i=3; i<5; i++)
do
execute some command 1
if command 2 is successful then do not run the command 1 (the for loop should continue)
if command 2 is not successful then run command 1 only once (like retry command 1 only once, after this the for loop should continue)
done
This is to note that command 2 is dependent on command 1 and command 2 can only be executed after command 1
for example:
for ( i=3; i<5; i++)
do
echo "i" >> mytext.txt ---> command 1
if "check the content of mytext.txt file to see if the value of i is actually added" ---> command 2
if it is not added then execute echo "i" >> mytext.txt (command 1) again and only once.
if i value is added to the file .. then exit and continue the loop
done
Since the "command 1" is quite big and not just an example echo statement here.I do not want to add "command 1" twice .. once outside and once inside the if condition. I want this logic in an optimized way with no redundancy of code.
Per a comment it sounds like the OP may need to invoke command 1 up to 2 times for a given $i value, but only wants to type command 1 once in the script.
Siddhartha's suggestion to use a function is probably good enough but depending on the actual command 1 (OP mentions that it's 'quite big') I'm going to play devil's advocate and assume there could be additional issues with passing some args to the function (eg, a need to escape some characters ... ??).
The general idea is to have an internal loop that can be executed at most 2 times, with logic in the loop that will allow for an 'early' exit (eg, after just one pass through the loop).
Since we're using pseudo-code I'll use the same ...
for ( i=3; i<5; i++ )
do
pass=1 # reset internal loop counter
while ( pass -le 2 )
do
echo "i" >> mytext.txt # command 1
if ( pass -eq 1 ) # after first 'command 1' execution
&& ( value of 'i' is in mytext.txt ) # command 2
then
break # break out of inner loop; alternatively ...
# pass=10 # ensure pass >= 2 to force loop to exit on this pass
fi
pass=pass+1 # on 1st pass set pass=2 => allows another pass through loop
# on 2nd pass set pass=3 => will force loop to exit
done
done
you can declare functions like
function command
{
your_command -f params
}
for ( i=3; i<5; i++)
do
if command ; then
echo "success"
else
echo "retry"
command
fi
done
I am using GNU bash version 4.4.12 and coming across an unusual situation. I am trying to pass an array by reference to a function. So the following code works as expected.
function test() {
local -n varK=${2}
local varJ=$(( ${1} + 10 ))
echo "${varJ}, ${varK[#]}"
}
varI=( 1 2 )
varJ=3
echo "result = '$( test 1 varI )'" # result = '11, 1 2'
echo "varI = '${varI[#]}'" # varI = '1 2'
echo "varJ = '${varJ}'" # varJ = '3'
The weird situation is that if I use the variable varI within the function, even if I define it as a local variable, then the variable varI gets clobbered.
function test() (
local -n varK=${2}
local varI=$(( ${1} + 10 ))
echo "${varI}, ${varK[#]}"
)
varI=( 1 2 )
varJ=3
echo "result = '$( test 1 varI )'" # result = '11, 11'
echo "varI = '${varI[#]}'" # varI = '1 2'
echo "varJ = '${varJ}'" # varJ = '3'
Does not the command local -n varK=${2} make a local copy of the array passed by reference? Also, if I am running the function in a subshell (and calling it as a subshell, should it not affect the parent process as all the documents claim?
The nameref doesn't know anything about the name it refers to; it is a simple alias. local -n varK=varI simply states that whenever you use the parameter name varK, pretend it is really varI, whatever that name means. By the time you use varK, varI is a local variable with the value 11, so that's what varK is as well. (Part of the confusion may also lie in how bash treats a non-array name used with array syntax; ${varI[#]} and ${varI} are equivalent whether or not the array attribute is set on the name.)
So in order to use varI within my function and still have access to referenced array, I made a local copy of the reference array:
local varJ=( "${varK[#]}" )
I want all variables names are set in shell script. I have a file which contains key value pairs and I was read content from that file and store/set into variables. I want to do some processes if a variable is available/set otherwise I don't need to do those processes. How to achieve this.
For example I run loop in shell scripts in each iteration it gives one of the variables is set before that command.
If code like this
a=test1
b=test2
c=test3
for i in ???
do
echo $i
done
then I want output like this
a
b
c
What command is used o achieve this.
You could use set before and after setting the variables
e.g:
$ set > aux1
$ c=345
$ set > aux2
$ diff aux1 aux2
57c57
< PIPESTATUS=([0]="141" [1]="0")
---
> PIPESTATUS=([0]="0")
112a113
> c=345
If you have a pre-defined list of such variables, then you can test it like this:
for i in $(echo "a b c"); do
echo $i
done
If i could help you :
#!/bin/sh
# Define list of tests
LIST_TESTS=`cat list_test.txt`
for TEST in ${LIST_TESTS}
do
vartest=`echo ${TEST}`
if [ "${vartest}" = "" ]
# No Test
then
echo "*** WARNING*** Test not found"
else
echo "${vartest} is available"
fi
done
# Second Define list of tests
tabTest=('test1' 'test2' 'test3')
i=0
while [ "${tabTest[$i]}" != "" ]
do
echo "${tabTest[$i]} is available"
i=$(($i+1))
done