Commands by derv82 (1)

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Execute a command on logout
Execute a command on shell logout,and run it until is finished,then shell is closed.

Adding Prefix to File name
Adding course name prefix to lecture pdfs

Get the time since epoch
Get the time since epoch. Useful when working with commands and logs which use this format.

find out how much space are occuipied by files smaller than 1024K
The command gives size of all files smaller than 1024k, this information, together with disk usage, can help determin file system parameter (e.g. block size) or storage device (e.g. SSD v.s. HDD). Note if you use awk instead of "cut| dc", you easily breach maximum allowed number of records in awk.

wget download with multiple simultaneous connections

print first n characters of any file in human readble form using hexdump
Usefull to determine unknown file type

check open ports without netstat or lsof

Scan a gz file for non-printable characters and display each line number and line that contains them.
Scans the file once to build a list of line numbers that contain non-printable characters Scans the file again, passing those line numbers to sed as two commands to print the line number and the line itself. Also passes the output through a tr to replace the characters with a ?

Get AWS temporary credentials ready to export based on a MFA virtual appliance
You might want to secure your AWS operations requiring to use a MFA token. But then to use API or tools, you need to pass credentials generated with a MFA token. This commands asks you for the MFA code and retrieves these credentials using AWS Cli. To print the exports, you can use: `awk '{ print "export AWS_ACCESS_KEY_ID=\"" $1 "\"\n" "export AWS_SECRET_ACCESS_KEY=\"" $2 "\"\n" "export AWS_SESSION_TOKEN=\"" $3 "\"" }'` You must adapt the command line to include: * $MFA_IDis ARN of the virtual MFA or serial number of the physical one * TTL for the credentials

Quickly build ulimit command from current values
It is helpful to know the current limits placed on your account, and using this shortcut is a quick way to figuring out which values to change for optimization or security. Alias is: $ alias ulimith="command ulimit -a|sed 's/^.*\([a-z]\))\(.*\)$/-\1\2/;s/^/ulimit /'|tr '\n' ' ';echo" Here's the result of this command: $ ulimit -c 0 -d unlimited -e 0 -f unlimited -i 155648 -l 32 -m unlimited -n 8192 -p 8 -q 819200 -r 0 -s 10240 -t unlimited -u unlimited -v unlimited -x unlimited $ ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 155648 max locked memory (kbytes, -l) 32 max memory size (kbytes, -m) unlimited open files (-n) 8192 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) unlimited virtual memory (kbytes, -v) unlimited file locks (-x) unlimited

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