lk/system/bash_tricks.md

title	tags
Terminal Tips	Documentation System

Track Live Changes

See changes in a file as it changes:

tail -f *somefile*

See changes in a directory, as it changes:

watch -d ls *directory*

Automatic Renaming

There are a bunch of files:

• Column CV.aux
• Column CV.log
• Column CV.out
• Column CV.pdf
• Column CV.tex
• tccv.cls

Goal: swap the word "Column" for "Alice" in all files.

IFS=$'\n'
for f in $(find . -name "Col*"); do
mv "$f" $(echo "$f" | sed s/Column/Alice/)
done

IFS is the field separator. This is required to denote the different files as marked by a new line, and not the spaces.

Arguments and Input

The rm' program takes arguments, but not stdin' from a keyboard, and therefore programs cannot pipe results into rm.

That said, we can sometimes pipe into rm with xargs rm' to turn the stdin into an argument. For example, if we have a list of files called list.txt' then we could use cat as so:

cat list.txt | xargs rm

... However, this wouldn't work if spaces were included, as rm would take everything literally.

Numbers

Add number to variables with:

• let "var=var+1"
• let "var+=1"
• let "var++"
• ((++var))
• ((var=var+1))
• ((var+=1))
• var=$(expr $var + 1)

((n--)) works identically.

Finding Duplicate Files

find . -type f -exec md5sum '{}' ';' | sort | uniq --all-repeated=separate -w 15 > all-files.txt

Output random characters

cat /dev/urandom | tr -cd [:alnum:] | dd bs=1 count=200 status=none && echo