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Posted by jpluimers on 2020/07/09
Various ways are explained at [WayBack] linux – How do I use sudo to redirect output to a location I don’t have permission to write to? – Stack Overflow.
Some are for simple commands and can be a one liner (for instance using tee, or executing a secondary shell).
Others are more suited for longer command sequences.
–jeroen
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Posted by jpluimers on 2020/06/17
Cool: you can return strings both as a function result, and by reference: they are explained in the question, second and fourth answer of [WayBack] How to return a string value from a Bash function – Stack Overflow.
Returning them by reference has two important benefits:
echo (normally used to return a result) for debugging purposesI also needed a bit of switch magic which I found at [WayBack] bash – Switch case with fallthrough? – Stack Overflow and array magic (from [WayBack] Array variables) as arrays are far more readable than indirection (on the why not, see [WayBack] BashFAQ/006 – Greg’s Wiki: How can I use variable variables (indirect variables, pointers, references) or associative arrays?).
So here is a function that returns a specific IPv4 octet.
function getIpv4Octet() {
IPv4=$1
octetIndex=$2
outputVariable=$3
slice="${IPv4}"
count=1
while [ "${count}" -le 4 ]
do
octet[${count}]="${slice%%.*}"
slice="${slice#*.}"
count=$((count+1))
done
case "${octetIndex}" in
"1" | "2" | "3" | "4")
;;
*)
octetIndex="4"
;;
esac
eval $outputVariable="${octet[$octetIndex]}"
}
You call it like this:
$ getIpv4Octet "192.168.178.32" 3 result && echo ${result}
178
–jeroen
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Posted by jpluimers on 2020/06/16
I needed to enumerate all the parameters to a function and access many of them by index in the same function, so thanks to both these:
I got at this:
declare -a arguments=("$@")
for index in ${!arguments[@]}; do
echo $index/${#arguments[@]}:${arguments[$index]}
done
These are all forms of Array handling or Shell Parameter Expansion with special cases for array variables:
! does indirection, in this case from the array to the index of the array# gets the lengt of the parameter (for arrays: the number of elements)[] acccesse an array variable using an indexVia:
–jeroen
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Posted by jpluimers on 2020/06/10
A while ago, I had to execute a series of aliases of which the names were stored in an array. A simple for loop with en eval call did the job.
Then I found out there are at least two more ways of evaluation in bash, so here are just a few links giving me a head start if I ever dig this up again:
Note that looping over parameters is different than over an array: [WayBack] Loop through an array of strings in Bash? – Stack Overflow
ou can use it like this:
## declare an array variable declare -a arr=("element1" "element2" "element3") ## now loop through the above array for i in "${arr[@]}" do echo "$i" # or do whatever with individual element of the array done # You can access them using echo "${arr[0]}", "${arr[1]}" alsoAlso works for multi-line array declaration
declare -a arr=("element1" "element2" "element3" "element4" )
–jeroen
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Posted by jpluimers on 2020/06/09
This is part of a bash alias where I had to use quadruple backslash in order to escape it for sed:
# The sed with quad //// is to prevent 'unterminated substitute in regular expression':
alias x='... | sed "s/=.*/ \\\\/"'
This is needed because bash will escape \\\\ into \\ which sed then escapes to \.
The easiest way to find this is to replace the sed with echo to see the expansion.
References:
–jeroen
Posted in *nix, *nix-tools, bash, bash, Development, Power User, Scripting, sed, Software Development | 2 Comments »
Posted by jpluimers on 2020/06/03
I read [WayBack] Cursor Movement earlier than [WayBack] Colours and Cursor Movement With tput and [WayBack] The Floating Clock Prompt.
So in one of my scripts I’ve now used an escape sequence, but I might change it to tput in a future version:
## Move one line up, then write finished scripts:
echo -e "\033[1A$finished\r"
I would probably have started with put if I had read [WayBack] bash – Set or change vertical position of the cursor – Stack Overflow first.
–jeroen
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Posted by jpluimers on 2020/06/02
I hardly do this, so I tend to forget that unset -f functionname deletes a function and unset variablename or unset -v variablename deletes a variable.
From:
I have done this:bash $ z() { echo ‘hello world’; }How do I get rid of it?
Source: [WayBack] How do I delete a Bash function? – Stack Overflow
Reference: [WayBack] unset Man Page – Bash – SS64.com
–jeroen
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Posted by jpluimers on 2020/05/21
Almost 20 years old, but still a very nice read [Archive.is] David Korn Tells All – Slashdot.
Another funny story involving David Korn during the not-so open source times of Microsoft late last century: [WayBack] Korn Shell Story
–jeroen
Posted in *nix, *nix-tools, bash, bash, Development, History, Power User, Scripting, Software Development | Leave a Comment »
Posted by jpluimers on 2020/05/12
For my reading list: Bash Notes for Professionals book
Download: [WayBack] BashNotesForProfessionals.pdf
Via: [WayBack] Bash Notes for Professionals – a book compiled from Stack Overflow Documentation released under Creative Commons BY-SA – ThisIsWhyICode – Google+
–jeroen
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Posted by jpluimers on 2020/04/22
[WayBack] Use the Unofficial Bash Strict Mode (Unless You Looove Debugging):
#!/bin/bashset -euo pipefailIFS=$'\n\t'
Explanation in the above post.
–jeroen
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The Wiert Corner - irregular stream of stuff 