Showing posts with label while. Show all posts
Showing posts with label while. Show all posts

Tuesday, 5 November 2013

My Linux Shell Cook-Book

How many times we struggle ourselves to remember how to write correctly a for loop in shell ?
When was the last time we did a search for string comparison in bash and test for a file timestamp?

My favourite treatment for weak memory or "shell syntax blackouts" is a simple text file called
MyBashCooks.txt which takes proudly always the first tab in Notepad++ when I am coding scripts.

I think it is void to mention that this small file is hand on the web and travels with me when I am visiting clients, generally, it is one of the very few things I have handy and don't move a second step without it.

The recipes in my cookbook share a common secret: single command line, so you can use them on the command prompt as is or break them in several lines inside your scripts.

I think we say too much on this, please enjoy and if you find a mistake, please drop me a line:

# If then else in a single line
r=ee; if [ "$r" == "" ] ;  then  echo "is null" ; else  echo "not null"; fi

# If then else ARITHMETIC Operations
x=0;if [ $x -eq 0 ]; then echo "x=0";else echo "other"; fi

# Check if word belongs to string and if it does, run a shell command 
# Compatible with all shells
string="this is a string "; word="str";test "${string#*$word}" != "$string" && echo "$word found in $string"

# Negative of the previous
string="this is a string "; word="xxx";test "${string#*$word}" != "$string" || echo "$word not found in $string"

# Combined case of found and not found....
string="this is a string "; word="xxx";test "${string#*$word}" != "$string" && echo "Executes when found." || echo "Executes when NOT found."

# single line while loop
while true; do  echo '----'; sleep 1 ; done

while true; do top -b -n 1  |  egrep  'top|Tasks|Cpu|Mem|Swap|PID|mysql' | grep -v root   ;sleep 10; echo '----' ; done

# single line for loop
for h in {app0,app1,app2,app3,index0,index1,index2,index3};  do echo $h; sleep 1;  done

# Tests the existence  of word in a string: works in all POSIX shells (bash, dash, korn...) 
string="my name is MyBighrase";word="e i"; echo "search [$word] in [$string]";test "${string#*$word}" != "$string" && echo "$word found in $string"

# From UNIX timestamp to date:
echo 1365436826 | gawk '{print strftime("%c", $0)}'

# From Date to timestamp:
date --date='04/04/2013 20:30:01' +"%s"

# Format Date output
date +"%m-%d-%y"

# Search for a string across directories with grep
find -RH theString /this/directory

# Serach for line numbers and cut a file only from line to line:
this one searches for all line numbers with date 20130607
cat  slow.log | grep -n 130607  
we get the lines of this date exists and isolate those numbers in a new file.
cat  slow.log | sed -n '16582739,17369638p' > slow_20130607.txt

# Monitoring Linux Processes

while true ; do top -b -n 1 -p 2163 >> mysql_3000.txt ; sleep 15 ;  done &

while true ; do date >> tmpfs_3000.txt ; df -h | grep mysql ; sleep 15 ;  done >> tmpfs_3000.txt &

while true ; do date >> process_3000.txt;  echo "show full processlist;" |  mysql -uroot -pmypass | grep -v Sleep >> process_3000.txt  ; sleep 15 ; done &