echo -e 'This is first string\nAnd this is second' > /path/to/file

echo "
str1
   $variable - why not?
str N
"

cat > ceph.conf << EOF
[global]
mon_host = xx.xx.xx.xx:6789
auth_cluster_required = cephx
auth_service_required = cephx
auth_client_required = cephx
EOF

├─bash───newgrp───bash───pstree

cp -r /opt/. /app

shopt -s extglob
rm -rf !(package*.json|node_modules) .[!.]* ..?*

если бла-бла-бла (вывод) | grep <expression> то выполнить <cmd>

echo "123" >/dev/tcp/127.0.0.1/7777

>/dev/tcp/127.0.0.1/23
bash: connect: Connection refused
bash: /dev/tcp/127.0.0.1/23: Connection refused

cut -c 140-240 file

hostname -I

cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 10 | sed 1q
base64 -w 15 /dev/urandom | head

? d????????? ? ? ? ?            ? .
? d????????? ? ? ? ?            ? ..
? -????????? ? ? ? ?            ? gpg.conf
? d????????? ? ? ? ?            ? openpgp-revocs.d
? -????????? ? ? ? ?            ? pubring.kbx
? -????????? ? ? ? ?            ? pubring.kbx~
? -????????? ? ? ? ?            ? trustdb.gpg

chmod -R a+X /path/to/folder

<SOME_DATA> | awk '{s+=$1}END{print s}'

nice find ./ -type f -mtime +365 | xargs du | awk '{ t+=$1 } END { print t }'

find ./ -type f -mtime +365 -exec ls {} \; 

nice find ./ -type f -mtime +365 -exec rm {} \; 

cmd=$(ps aux)
printf "%s\n" "$cmd"

for i in $(ls *.back); do echo $i is now ${i/back/hi-bo0om}; done
1.2.back is now 1.2.hi-bo0om
3.4.back is now 3.4.hi-bo0om
5.6.back is now 5.6.hi-bo0om

find -type f -name "*.html~" |
while read f; do
    mv "$f" "${f%\~}"
done

for i in $(ls *.back); do basename $i .back; done

basename -s .back $(find ./ -name *.back)