I'm setting my prompt inside of .bash_profile like this
export PS1="\w\$(getBranchName)\n ---->"
My getBranchName function exists, and this works, fine.
My question is, why do I need to escape the call to getBranchName like this \$(getBranchName).
In other words, why doesn't this code work, instead?
export PS1="\w$(getBranchName)\n ---->"
If curious, this is what the getBranchName function looks like
esc="\033"
redf="${esc}[31m"
green="${esc}[32m"
purple="${esc}[35m"
cyanf="${esc}[36m"
reset="${esc}[0m"
getBranchName() {
if [[ "$(__git_ps1 '%s')" == "master" ]]
then
echo -e "${redf}$(__git_ps1)${reset}";
else
echo -e "${cyanf}$(__git_ps1)${reset}";
fi
}
export PS1="\w\$(getBranchName)\n ---->"
You need to escape the dollar because you want to store this exact text in your variable.
Try it by typing echo "$PS1". You should see the exact text : \w$(getBranchName)\n ---->
If you didn't escape it, the function would be evaluated only once, during the allocation.
The bottom line is that PS1 is a special variable : every time you display a new line in the console, the variable is evaluated to extract the display settings.
The PS1 variable is basically a template string (which might contain function calls) which is evaluated each time the prompt is shown.
If you want to evaluate a function each time, so that each prompt shows the result of this new execution, you need to escape the call.
If you would embed the function call directly in the string, the function would be called once immediately (i.e. likely during login) and your PS1 will contain the result of this single function call as evaluated during your initial login. Thus, the value won't be updated again since the function is not called anymore (since the PS1 doesn't contain the function call anymore but only the static result of one).
It's escaped because you want it to run when the shell evaluates $PS1 each time it's displayed, not just during the assignment.
The other expansions (which should be using tput unless you actually like random control codes all over your non-ANSI terminals) you want to be expanded just once, when you assign to PS1.
I am trying to strip the string value in the variable and copy to another variable using bash parameter expansion.
initialModified=${initial#abc}
This give me the value in initialModified after stripping out abc from the beginning of the string in initial variable when I echo initialModified.
However, along with this I would like to add required check
initialModified=${initial#abc:?Required parameter}
This doesn't work as expected. And throws an error.
Any help is appreciated.
I am beginner to Shell scripting.
I have used a variable to store value A="MyScript". I tried to concatenate the string in subsequent steps $A_new. To my surprise it didn't work and $A.new worked.
Could you please help me in understanding these details?
Thanks
Shell variable names are composed of alphabetic characters, numbers and underscores.
3.231 Name
In the shell command language, a word consisting solely of underscores, digits, and alphabetics from the portable character set. The first character of a name is not a digit.
So when you wrote $A_new the shell interpreted the underscore (and new) as part of the variable name and expanded the variable A_new.
A period is not valid in a variable name so when the shell parsed $A.new for a variable to expand it stopped at the period and expanded the A variable.
The ${A} syntax is designed to allow this to work as intended here.
You can use any of the following to have this work correctly (in rough order of preferability):
echo "${A}_new"
echo "$A"_new
echo $A\_new
The last is least desirable because you can't quote the whole string (or the \ doesn't get removed. So since you should basically always quote your variable expansions you would end up probably doing echo "$A"\_new but that's no different then point 2 ultimately so why bother.
This happens because the underscore is the valid character in variable names.
Try this way:
${A}_new or "$A"_new
The name of a variable can contain letters ( a to z or A to Z), numbers ( 0 to 9) or the underscore character ( _).
Shell does not require any variable declaration as in programming languages as C , C++ or java. So when you write $A_new shell consider A_new as a variable, which you have not assigned any value therefore it comes to be null.
To achieve what you mentioned use as :
${A}_new
Its always a good practice to enclose variable names in braces after $ sign to avoid such situation.
The following script is showing me "unexpected end of file" error. I have no clue why am I facing this error. My all the quotes are closed properly.
#!/usr/bin/sh
insertsql(){
#sqlite3 /mnt/rd/stats_flow_db.sqlite <<EOF
echo "insert into flow values($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13,$14,$15,$16,$17,$18)"
#.quit
}
for i in {1..100}
do
src_ip = "10.1.2."+$i
echo $src_ip
src_ip_octets = ${src_ip//,/}
src_ip_int = $src_ip_octets[0]*1<<24+$src_ip_octets[1]*1<<16+$src_ip_octets[2]*1<<8+$src_ip_octets[3]
dst_ip = "10.1.1."+$i
dst_ip_octets = ${dst_ip//,/}
dst_ip_int = $dst_ip_octets[0]*1<<24+$dst_ip_octets[1]*1<<16+$dst_ip_octets[2]*1<<8+$dst_ip_octets[3]
insertsql(1, 10000, $dst_ip, 20000, $src_ip, "2012-08-02,12:30:25.0","2012-08-02,12:45:25.0",0,0,0,"flow_a010105_a010104_47173_5005_1_50183d19.rrd",0,12,$src_ip_int,$dst_ip_int,3,50000000,80000000)
done
That error is caused by <<. When encountering that, the script tries to read until it finds a line which has exactly (starting in the first column) what is found after the <<. As that is never found, the script searches to the end and then complains that the file ended unexpectedly.
That will not be your only problem, however. I see at least the following other problems:
You can only use $1 to $9 for positional parameters. If you want to go beyond that, the use of the shift command is required or, if your version of the shell supports it, use braces around the variable name; e.g. ${10}, ${11}...
Variable assignments must not have whitespace arount the equal sign
To call your insertsql you must not use ( and ); you'd define a new function that way.
The cass to your insertsql function must pass the parameters whitespace separated, not comma separated.
A couple of problems:
There should be no space between equal sign and two sides of an assignment: e.g.,: dst_ip="10.1.1.$i"
String concatenation is not done using plus sign e.g., dst_ip="10.1.1.$i"
There is no shift operator in bash, no <<: $dst_ip_octets[0]*1<<24 can be done with expr $dst_ip_octets[0] * 16777216 `
Functions are called just like shell scripts, arguments are separated by space and no parenthesis: insertsql 1 10000 ...
That is because you don't follow shell syntax.
To ser variable you are not allowed to use space around = and to concatenate two parts of string you shouldn't use +. So the string
src_ip = "10.1.2."+$i
become
src_ip="10.1.2.$i"
Why you're using the string
src_ip_octets = ${src_ip//,/}
I don't know. There is absolutely no commas in you variable. So even to delete all commas it should look like (the last / is not required in case you're just deleting symbols):
src_ip_octets=${src_ip//,}
The next string has a lot of symbols that shell intepreter at its own way and that's why you get the error about unexpected end of file (especially due to heredoc <<)
src_ip_int = $src_ip_octets[0]*1<<24+$src_ip_octets[1]*1<<16+$src_ip_octets[2]*1<<8+$src_ip_octets[3]
So I don't know what exactly did you mean, though it seems to me it should be something like
src_ip_int=$(( ${src_ip_octets%%*.}+$(echo $src_ip_octets|sed 's/[0-9]\+\.\(\[0-9]\+\)\..*/\1/')+$(echo $src_ip_octets|sed 's/\([0-9]\+\.\)\{2\}\(\[0-9]\+\)\..*/\1/')+${src_ip_octets##*.} ))
The same stuff is with the next strings.
You can't do this:
dst_ip_int = $dst_ip_octets[0]*1<<24+$dst_ip_octets[1]*1<<16+$dst_ip_octets[2]*1<<8+$dst_ip_octets[3]
The shell doesn't do math. This isn't C. If you want to do this sort of calculation, you'll need to use something like bc, dc or some other tool that can do the sort of math you're attempting here.
Most of those operators are actually shell metacharacters that mean something entirely different. For example, << is input redirection, and [ and ] are used for filename globbing.
Nested variables have prevented me from trying to use BASH more extensively... consider the following:
export SYS_DIR='/home/${LOGNAME}/sys'
export APP_DIR='${SYS_DIR}/app'
I always end up with
> set
APP_DIR=/home/${LOGNAME}/sys/app
why? lol
and how do I get what I want =/
I'm not trying to resolve ${${var}}, but rather actual strings as shown above
Use double quotes
export APP_DIR="${SYS_DIR}/app"
Single quotes treat everything inside as literal, not evaluated.