bash - animeshtrivedi/notes GitHub Wiki

sudo sh -c '/usr/bin/echo 3 > /proc/sys/vm/drop_caches'

from=1
to=46
dev_str=""
for (( i = $from; i < $to; i++)) do 
        echo $i
        dev_str+="/dev/nvme${i}n1:"
done
final=${dev_str::-1}
echo $final 

echo $'\t'"I am $USER"

Echo tab characters in bash script

https://stackoverflow.com/questions/52277264/convert-doc-to-docx-using-soffice-not-working

soffice --headless --convert-to docx test.pdf 
Error: no export filter for /home/atr/Downloads/rocksdb-benchmark-tuning-guide-on-xeon.docx found, aborting.
Error: no export filter

Just open in the office.

tar -czvf filename.tar.gz /path/to/dir1 dir2 dir3 

extract in the /tmp folder

tar -xzvf projects.tar.gz -C /tmp/

# match lines containing numbers 
grep -E -i [0-9]+
# that also contain blk keyword 

https://www.cyberciti.biz/faq/grep-regular-expressions/

: ' 
Here 
it 
is 
'

.ssh/config example: Both keys needs (first, and second) to be on the local machine

Host host 
	Hostname a.b.c.d 
	ProxyJump JumpSrv 
	User atr2
	IdentityFile ~/.ssh/second 

Host JumpSrv 
	HostName w.x.y.z
	User atr1
	IdentityFile ~/.ssh/first 
	IdentitiesOnly yes

Note: make sure to use the right key extension id_rsa not id_rsa.pub otherwise cryptic messages.

debug1: Trying private key: id_rsa
Load key "id_rsa": error in libcrypto
debug2: we did not send a packet, disable method
debug3: authmethod_lookup password

$ sudo /home/animesh.trivedi/src/ubdsrv/ublk add -t loop –f /dev/nullb0 -q 16 d 512
start dev 0 daemon failed, ret -1
$ sudo /home/animesh.trivedi/src/ubdsrv/ublk add -t loop -f /dev/nullb0 -q 16 d 512
dev id 0: nr_hw_queues 16 queue_depth 128 block size 512 dev_capacity 67108864

https://www.babelstone.co.uk/Unicode/whatisit.html

# all output and show it 
SomeCommand 2>&1 | tee log.txt

#all to a file 
SomeCommand &>./log.txt 

#discard stderr 
SomeCommand 2>/dev/null

https://askubuntu.com/questions/22037/aliases-not-available-when-using-sudo

alias sudo='sudo '

From the bash manual:

Aliases allow a string to be substituted for a word when it is used as the first word of a simple command. The shell maintains a list of aliases that may be set and unset with the alias and unalias builtin commands.

The first word of each simple command, if unquoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias. The characters ‘/’, ‘$’, ‘`’, ‘=’ and any of the shell metacharacters or quoting characters listed above may not appear in an alias name. The replacement text may contain any valid shell input, including shell metacharacters. The first word of the replacement text is tested for aliases, but a word that is identical to an alias being expanded is not expanded a second time. This means that one may alias ls to "ls -F", for instance, and Bash does not try to recursively expand the replacement text. If the last character of the alias value is a space or tab character, then the next command word following the alias is also checked for alias expansion.

(Emphasis mine). Bash only checks the first word of a command for an alias, any words after that are not checked. That means in a command like sudo ll, only the first word (sudo) is checked by bash for an alias, ll is ignored. We can tell bash to check the next word after the alias (i.e sudo) by adding a space to the end of the alias value.

sshfs atr@localhost:/home/atr/ ./vm-qemu7777/ -p 7777

sudo -E env "PATH=$PATH" <command> [arguments]
sudo env "PATH=$PATH" <command> [arguments]

• https://stackoverflow.com/questions/12996397/command-not-found-when-using-sudo
• https://unix.stackexchange.com/questions/83191/how-to-make-sudo-preserve-path

$ sudo apt-get install librsvg2-bin
$ rsvg-convert -f pdf -o t.pdf t.svg

in a loop

for f in *; do rsvg-convert -f pdf -o ${f%%.*}.pdf ${f%%.*}.svg; done

https://superuser.com/questions/381125/how-do-i-convert-an-svg-to-a-pdf-on-linux

for f in *; do echo ${f%%.*}; done

https://stackoverflow.com/questions/7119223/file-name-without-extension-in-bash-for-loop

convert *.png file.pdf 

https://askubuntu.com/questions/158093/how-do-i-convert-a-png-to-pdf-with-only-the-default-packages-on-11-10

awk 'NF' filename 

https://stackoverflow.com/questions/16414410/delete-empty-lines-using-sed

lets say 3rd

awk 'NR % 3 == 0' file.txt

https://unix.stackexchange.com/questions/369181/printing-every-nth-line-out-of-a-large-file-into-a-new-file/369220

grep -f inputfile.txt inputfile2.txt 

https://stackoverflow.com/questions/21287389/how-to-find-words-from-one-file-in-another-file

$ dpkg -S /bin/ls
coreutils: /bin/ls

https://www.redhat.com/sysadmin/manage-multiple-ssh-key-pairs

https://czarpino.medium.com/how-to-tell-git-which-ssh-key-to-use-c8574fb243fd

convert input.jpg -rotate 180 out.jpg

https://unix.stackexchange.com/questions/365592/how-to-rotate-a-set-of-pictures-from-the-command-line

convert -compress jpeg *.jpg my-jpegs.pdf

https://stackoverflow.com/questions/4234164/bash-convert-to-pdf/16325857

Security error about authorization: https://askubuntu.com/questions/1081895/trouble-with-batch-conversion-of-png-to-pdf-using-convert

Comment out this line: <policy domain="coder" rights="none" pattern="PDF" /> in /etc/ImageMagick-6/policy.xml

for i in *pdf ; do pdftk "$i" cat 2-end output "trimmed/$i" ; done

https://askubuntu.com/questions/146375/remove-only-1st-page-from-a-lot-of-pdf-files

https://www.cyberciti.biz/faq/unix-linux-check-if-port-is-in-use-command/

sudo lsof -i -P -n | grep LISTEN 

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

• -dPDFSETTINGS=/screen lower quality, smaller size. (72 dpi)
• -dPDFSETTINGS=/ebook for better quality, but slightly larger pdfs. (150 dpi)
• -dPDFSETTINGS=/prepress output similar to Acrobat Distiller "Prepress Optimized" setting (300 dpi)
• -dPDFSETTINGS=/printer selects output similar to the Acrobat Distiller "Print Optimized" setting (300 dpi)
• -dPDFSETTINGS=/default selects output intended to be useful across a wide variety of uses, possibly at thee expense of a larger output file https://askubuntu.com/questions/113544/how-can-i-reduce-the-file-size-of-a-scanned-pdf-file

Rotating:

First 9 pages

pdftk xxx.pdf cat 1-9north output xxx2.pdf

https://makandracards.com/makandra/1487-rotate-a-pdf-under-ubuntu-linux

find vector/ -type f -exec sed -i 's/BitVectorHelper.setValidityBit(validityBuffer, thisIndex, from.isSet(fromIndex));/setValidityBit(thisIndex, from.isSet(fromIndex));/g' {} \;

find /path/to/files -type f -exec sed -i 's/oldstring/new string/g' {} \;

https://stackoverflow.com/questions/15402770/how-to-grep-and-replace

Modifies the time for every file. Hence, some IDE or build systems might get confused.

cat items | xargs -I % git clone --mirror %

https://unix.stackexchange.com/questions/3593/using-xargs-with-input-from-a-file

~.

https://www.cyberciti.biz/faq/openssh-linux-unix-osx-kill-hung-ssh-session/

2>&1 

(notice the negation !)

if [[ ! $id ]]; 
    echo "$id is empty"
fi

while IFS='' read -r line || [[ -n "$line" ]]; do
    echo "Text read from file: $line"
done < "$1"

https://stackoverflow.com/questions/10929453/read-a-file-line-by-line-assigning-the-value-to-a-variable

#!/bin/bash
# Tested using bash version 4.1.5
for ((i=1;i<=100;i++));
do
# your-unix-command-here
echo $i
done

you can replace * with some pattern matching

for entry in "$search_dir"/*
do
  echo "$entry"
done

https://stackoverflow.com/questions/3522341/identify-user-in-a-bash-script-called-by-sudo

#!/bin/bash
if [[ $EUID -ne 0 ]]; then
   echo "This script must be run as root" 
   exit 1
fi

https://askubuntu.com/questions/15853/how-can-a-script-check-if-its-being-run-as-root