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• Bash - how can i pass variable to command and read its output

  - by Skuja

  In my bash script i want to execute command that will find lines in a file that starts with a keyword which is stored in a variable like this: keyword="key" result=(`cat path/to/my/file | grep '^$keyword'`)

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• WEB based HPC cluster node management

  - by Skuja

  Hello, i am working on my school diploma thesis. The main goal is to create web based application where logged users could see free and busy nodes, turn them on and off, see what process they are running etc. Figured out that i could do something like this - write some cron daemon that would run every 30seconds or so, and it could run ping utility for each node to find out if it is on or off, then write results to some file. Then from my web app (i will write in PHP) i could read the info. Will it be a good solution? How would you suggest me to do it? And finally, is there any existing solutions (it may not be a definetly ewb based) for managment of cluster nodes?

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• Escape characters contained by bash variable in regex pattern

  - by Skuja

  In my bash script, i am trying to execute following Linux command: sed -i "/$data_line/ d" $data_dir $data_line is entered by user and it may conatain special characters that could brake regex. How can i escape all of the possible special characters in $data_line before i execute sed command?

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• Check which nodes of Beowulf HPC cluster system are free from PHP app?

  - by Skuja

  I am working on my diploma thesis project. I have access to 32Node Dell poweredge HPC cluster system with Linux(Debian i think) installed on it. My first goal is to create web (PHP) app where logged users could see free and busy nodes, turn them on and off. I am planning to do something like this - write some cron daemon that would run every 30seconds or other interval, and it could run ping utility for each node to find out if it is on or off, then write results to some file. Then from my web app i could read the info. Will it be a good solution? What existing for node management solutions are there?

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• C - How can i get return value of command passed to execl?

  - by Skuja

  I know that it is possible to read commands output with a pipe? But what about getting return value ? For example i want to execute: execl("/bin/ping", "/bin/ping" , "-c", "1", "-t", "1", ip_addr, NULL); How can i get returned value of ping command to find out if it returned 0 or 1?

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• MySQL count problem

  - by Skuja

  I have 3 tables users(id,name),groups(id,name) and users_groups(user_id,group_id). users and groups have many to many relationship, so the third one is for storing users and groups relations. I would like to select all the data from groups with user count in each group. So far I came up with this: SELECT groups.*, COUNT(users_groups.user_id) AS user_count FROM groups LEFT JOIN users_groups ON users_groups.group_id = groups.id The problem is that query result is not returning any of groups which has no users (users_groups doesnt have any records with group_id of those groups). How should I create my query to select all the groups and they user count, or user count as 0 if there are no users for that group?

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• c, pass awk syntax as argument to execl

  - by Skuja

  I want to run following command in c to read systems cpu and memory usage: ps aux|awk 'NR > 0 { cpu +=$3; ram+=$4 }; END {print cpu,ram}' I am trying to pass it to execl command and after that read its output: execl("/bin/ps", "/bin/ps", "aux|awk", "'NR > 0 { cpu +=$3; ram+=$4 }; END {print cpu,ram}'",(char *) 0); but in terminal i am getting following error: ERROR: Unsupported option (BSD syntax) I would like to know how to properly pass awk as argument to execl?

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