I have a string in a variable Var.
And the value looks like this:
Var="Key1:Val1~Key2:Val2~"
I just simply need this split by "~" and assigned to an array in KSH only
When I try Var2=$(echo $Var | sed $'s/~/\\n/g')
and check the size of Var2 array as follows:
ArrSize=${#Var2[#]}
I always get 1. I would have imagined that would be 2. Please Help
Assuming you want to use the x=( list of array items ) method of populating the array then you need to wrap the right side of the assignment in a pair of parens, eg:
$ Var2=( $( echo $Var | sed $'s/~/\\n/g' ) )
$ typeset -p Var2
typeset -a Var2=(Key1:Val1 Key2:Val2)
$ echo "${#Var2[#]}"
2
Other options that accomplish the same thing but reduce the overhead of subprocess calls:
here string:
$ Var2=( $(sed 's/~/ /g' <<< "${Var}") )
$ typeset -p Var2
typeset -a Var2=(Key1:Val1 Key2:Val2)
$ echo "${#Var2[#]}"
2
parameter substitution:
$ Var2=( ${Var//\~/ } )
$ typeset -p Var2
typeset -a Var2=(Key1:Val1 Key2:Val2)
$ echo "${#Var2[#]}"
2
NOTE: while ${var//~/ } works in ksh, other shells (eg, bash) require the ~ to be escaped (ie, \~); ksh appears to work with both - ~ and \~ = so I've updated the answer to include the escape
I'm new to bash.
I want to convert below alias command form tcsh to bash:
alias buzz 'echo \!$;if (-e ~/.sshelp.txt) grep -i \!$ ~/.sshelp.txt && echo \!$;if (-e ~/.sshelp_qct.txt) grep -i \!$ ~/.sshelp_qct.txt '
I tried below command but it doesn't work. Any suggestions?
alias buzz= 'echo \!$;if (-e ~/.sshelp.txt) grep -i \!$ ~/.sshelp.txt && echo \!$;if (-e ~/.sshelp_qct.txt) grep -i \!$ ~/.sshelp_qct.txt '
Define a function in bash. C shells define aliases because they don't support functions. I think the following is (roughly) equivalent.
buzz () {
echo "$1"
if [ -e ~/.sshelp.txt ]; then
grep -i "$1" ~/.sshelp.txt && echo "$1"
fi
echo "$1"
if [ -e ~/.sshelp_qct.txt ]; then
grep -i "$1" ~/.sshelp_qct.txt
fi
}
I would like to run commands such as "history" or "!23" off of a pipe.
How might I achieve this?
Why does the following command not work?
echo "history" | xargs eval $1
To answer (2) first:
history and eval are both bash builtins. So xargs cannot run either of them.
xargs does not use $1 arguments. man xargs for the correct syntax.
For (1), it doesn't really make much sense to do what you are attempting because shell history is not likely to be synchronised between invocations, but you could try something like:
{ echo 'history'; echo '!23'; } | bash -i
or:
{ echo 'history'; echo '!23'; } | while read -r cmd; do eval "$cmd"; done
Note that pipelines run inside subshells. Environment changes are not retained:
x=1; echo "x=2" | while read -r cmd; do eval "$cmd"; done; echo "$x"
You can try like this
First redirect the history commands to a file (cut out the line numbers)
history | cut -c 8- > cmd.txt
Now Create this script hcmd.sh(Referred to this Read a file line by line assigning the value to a variable)
#!/bin/bash
while IFS='' read -r line || [[ -n "$line" ]]; do
echo "Text read from file: $line"
$line
done < "cmd.txt"
Run it like this
./hcmd.sh
I'm trying to populate an associative array with the output of a command. I can do it without a command as:
$ declare -A x=( [first]=foo [second]=bar )
$ echo "${x[first]}, ${x[second]}"
foo, bar
and I can populate a non-associative array with command output as:
$ declare y=( $(echo 'foo bar') )
$ echo "${y[0]}, ${y[1]}"
foo, bar
but when I try to build on both of the above to create a statement that will populate an associative array from a command, I get the following error message:
$ declare -A z=( $(echo '[first]=foo [second]=bar') )
-bash: z: $(echo '[first]=foo [second]=bar'): must use subscript when assigning associative array
Why am I getting that error message and what is the correct syntax to populate an associative array with the output of a command? I am trying to avoid using eval for the usual reasons, do not want to use a temp file, and of course echo is just being used as an example of a command that produces the effect in question, the real command will be more complicated.
So, based on a couple of the answers below, it looks like it was just my quoting that was a problem:
$ declare -A z="( $(echo '[first]=foo [second]=bar') )"
$ echo "${z[first]}, ${z[second]}"
foo, bar
and with spaces in the indices and values:
$ declare -A z="( $(echo '[first field]="foo with space" [second]="space bar"') )"
$ echo "${z[first field]}, ${z[second]}"
foo with space, space bar
EDIT in response to a question in the comments about why the quotes are necessary (How do I populate a bash associative array with command output?) - I don't exactly know but maybe someone else can explain using the results of this script as reference (not expecting the specified indices to be used in the indexed arrays, they're just part of the strings being populated as the array values):
$ cat tst.sh
#!/bin/env bash
set -x
printf 'Indexed, no quotes\n'
declare -a w=( $(echo '[first]=foo [second]=bar') )
declare -p w
printf '\n---\n'
printf 'Indexed, with quotes\n'
declare -a x="( $(echo '[first]=foo [second]=bar') )"
declare -p x
printf '\n---\n'
printf 'Associative, no quotes\n'
declare -A y="( $(echo '[first]=foo [second]=bar') )"
declare -p y
printf '\n---\n'
printf 'Associative, with quotes\n'
declare -A z=( $(echo '[first]=foo [second]=bar') )
declare -p z
.
$ ./tst.sh
+ printf 'Indexed, no quotes\n'
Indexed, no quotes
+ w=($(echo '[first]=foo [second]=bar'))
++ echo '[first]=foo [second]=bar'
+ declare -a w
+ declare -p w
declare -a w=([0]="[first]=foo" [1]="[second]=bar")
+ printf '\n---\n'
---
+ printf 'Indexed, with quotes\n'
Indexed, with quotes
++ echo '[first]=foo [second]=bar'
+ declare -a 'x=( [first]=foo [second]=bar )'
+ declare -p x
declare -a x=([0]="bar")
+ printf '\n---\n'
---
+ printf 'Associative, no quotes\n'
Associative, no quotes
++ echo '[first]=foo [second]=bar'
+ declare -A 'y=( [first]=foo [second]=bar )'
+ declare -p y
declare -A y=([second]="bar" [first]="foo" )
+ printf '\n---\n'
---
+ printf 'Associative, with quotes\n'
Associative, with quotes
+ z=($(echo '[first]=foo [second]=bar'))
./tst.sh: line 24: z: $(echo '[first]=foo [second]=bar'): must use subscript when assigning associative array
+ declare -A z
+ declare -p z
declare -A z=()
Here is a traditional while loop approach to populate an associative array from a command's output:
while IFS= read -r; do
declare -A z+="( $REPLY )"
done < <(printf '[first]=foo [second]=bar\n[third]=baz\n')
# check output
$> echo "${z[first]}, ${z[second]}, ${z[third]}"
foo, bar, baz
# or declare -p
$> declare -p z
declare -A z='([third]="baz" [second]="bar" [first]="foo" )'
EDIT: Your original attempt will also work with proper quotes:
$> unset z
$> declare -A z="( $(echo '[first]=foo [second]=bar') )"
$> declare -p z
declare -A z='([second]="bar" [first]="foo" )'
I imagine this is somewhat brittle, but you can make the entire z=(...) assignment the result of a command substitution.
declare -A "$(echo z="($(echo '[first]=foo [second]=bar'))")"
Given that this works:
declare -A z=([first]=$(echo 'foo') [second]=$(echo 'bar'))
I'm guessing that Bash needs to see the associative array initialization list before doing any substitutions. So I don't see a way to avoid eval:
eval "declare -A z=($(echo '[first]=foo [second]=bar'))"
What is a "usual reason" to avoid eval?
I'm trying to write a bash script that iterates over the arguments and builds a string like the following:
Usage:
./myScript a b c d
Expected output:
-e "a" -e "b" -e "c" -e "d"
The script looks like the following:
#!/bin/bash
pattern=""
for arg in "$#" do
pattern=$pattern" -e \"$arg\""
done
echo $pattern
The actual output misses the first -e, i.e., the output is:
"a" -e "b" -e "c" -e "d"
What am I doing wrong? What is the correct way to append -e?
You are doing nothing wrong. It is just that echo takes -e as an argument *.
$ pattern='-e asdf -e ghjk'
$ echo $pattern
asdf -e ghjk
If you quote the variable it works as expected.
$ echo "$pattern"
-e asdf -e ghjk
* man echo
-e enable interpretation of backslash escapes