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
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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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Posted by jpluimers on 2020/04/20
Since I tend to forget this:
More info at:
I think for functions, you can apply what is linked from Some useful links on bash parameters: $1, $*, $@, quotes, etc., so a loop over all parameters in a function is the same as in a script, see [WayBack] shell – how to loop through arguments in a bash script – Unix & Linux Stack Exchange from Gilles:
There’s a special syntax for this:
for i do echo "$i" doneMore generally, the list of parameters of the current script or function is available through the special variable
$@.for i in "$@"; do echo "$i" doneNote that you need the double quotes around
$@, otherwise the parameters undergo wildcard expansion and field splitting."$@"is magic: despite the double quotes, it expands into as many fields as there are parameters.print_arguments () { for i in "$@"; do echo "$i"; done } print_arguments 'hello world' '*' 'special !\characters' # prints 3 lines print_arguments '' # prints one empty line print_arguments # prints nothing
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Posted by jpluimers on 2020/03/17
From [WayBack] bash – How to add a progress bar to a shell script? – Stack Overflow (thanks Mitch Haile!):
You can implement this by overwriting a line. Use
\rto go back to the beginning of the line without writing\nto the terminal.Write
\nwhen you’re done to advance the line.Use
echo -neto:
- not print
\nand- to recognize escape sequences like
\r.Here’s a demo:
echo -ne '##### (33%)\r' sleep 1 echo -ne '############# (66%)\r' sleep 1 echo -ne '####################### (100%)\r' echo -ne '\n'
–jeroen
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Posted by jpluimers on 2020/02/18
Excellent answer at [WayBack] linux – Bash: Command grouping (&&, ||, …) – Stack Overflow by Charles Duffy:
Operator precedence for
&&and||is strictly left-to-right.Thus:
pwd; (ls) || { cd .. && ls student/; } && cd student || cd / && cd ;…is equivalent to…
pwd; { { { (ls) || { cd .. && ls student/; }; } && cd student; } || cd /; } && cd ; }…breaking that down graphically:
pwd; { # 1 { # 2 { (ls) || # 3 { cd .. && # 4 ls student/; # 5 }; # 6 } && cd student; # 7 } || cd /; # 8 } && cd ; # 9
pwdhappens unconditionally- (Grouping only)
lshappens (in a subshell) unconditionally.cd ..happens if (3) failed.ls student/happens if (3) failed and (4) succeeded- (Grouping only)
cd studenthappens if either (3) succeeded or both (4) and (5) succeeded.cd /happens if either [both (3) and one of (4) or (5) failed], or [(7) failed].cdhappens if (7) occurred and succeeded, or (7) occurred and succeeded.
Using explicit grouping operators is wise to avoid confusing yourself. Avoiding writing code as hard to read as this is even wiser.
–jeroen
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Posted by jpluimers on 2019/12/03
Many unix tools that report sizes in bytes can convert them to either IEC or SI readable formats.
For github.com/jpluimers/btrfs-du/blob/master/btrfs-du I wrote about last week, I also wanted that kind of behaviour. So I did some research and came up with the code and test cases below.
Note that depending on the bitness of your system, bash integer numeric values are limited in size; see [WayBack] What is the maximum value of a numeric bash shell variable? – Super User.
So I wrote a small
bashscript for that too, which needed also gave me the opportunity to show how a perpetual while loop as explained by [WayBack] bash – “while :” vs. “while true” – Stack Overflow.Two things that always bite me with these short scripts are expressions (done through [WayBack]Arithmetic Expansion) and comparisons (through[WayBack] Other Comparison Operators).
The IEC suffixes contain one extra i to indicate binary and – next to the ISO notation that were already ISO defined – made it into the ISO 80000 standard since 2008. Here is a comparison list from [WayBack] Binary prefix – Wikipedia:
Most tools nowadays default to binary IEC suffixes for byte sizes, though disk manufacturers still use SI suffixes because, well then they appear bigger but aren’t. Just for comparison, look at the numbers from [WayBack] File size – Wikipedia and [WayBack] IEC and SI Size Notations – AN!Wiki where I got the test cases from:
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Posted by jpluimers on 2019/11/26
Hopefully I’ve been able to integrate some of the ideas in the links below in github.com/jpluimers/btrfs-du/blob/master/btrfs-du
One of the features I wanted there was to be able to add optional switches like --raw, --iec or --si to it similar to what as the btrfs qgroup show subcommand has.
It seems possible with bash, but it is not trivial, at least not for me as a non-frequent bash user, so here are some links to get me started:
In retrospect, other languages than bash might have been a better choice for a script like that (:
–jeroen
PS, some btrfs references:
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The Wiert Corner - irregular stream of stuff 