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Recently I had the requirement to allow multiple containers of the same application to be run on a single development server. This requirement drastically changed how we retrieve logs over SSH from the servers, and because I am not extremely well versed in bash, I wanted to get this script reviewed to see if there is an easier/cleaner way to approach this problem.

The goal of the script is to produce a single log file on the local system for each container on that is running on the remote server. It is currently working as expected for 1 and N containers running on a single server.

The script I wrote does the following:

  1. Verify that the server being requested can provide the logs
  2. SSH into the remote server and save the logs for each container to a file on the local system
  3. Post-Process the logs into individual log files for each container that is present

I am fairly certain there is a much easier way to accomplish this task, hence the post here to see if anyone can point me in the right direction (I have a feeling, as I write this, that I can just scp the docker log files for each container to the local system instead of all of this.... But I also want to practice some bash, so I would still like this reviewed)

Script:

#!/bin/bash

# Add a help parameter to the script
if [ "$1" == "-h" ] || [ "$1" == "-help" ]; then
    echo "Usage: $(basename "$0")"
    echo " Logs will be placed in /c/temp/logs/<server>.log"
    echo " Prompts:"
    echo "  - Username: AD Username for Logins"
    echo "  - Server: This is a dev server, valid choices are:"
    echo "      (<SERVER_NAME>1 <SERVER_NAME>2 <SERVER_NAME>3 <SERVER_NAME>4)"
    exit 0
fi

# Create an array of valid servers to check for logs
servers=(<SERVER_NAME>1 <SERVER_NAME>2 <SERVER_NAME>3 <SERVER_NAME>4)

# Ask the user where they want to get the logs from
read -rp "Username: " user
read -rp "Server: " server

# Validate the server can retrieve logs
foundServer=0
for i in "${servers[@]}"; do
    if [ "$i" == "$server" ]; then
        foundServer=1
        break
    fi
done

if [ $foundServer == 0 ]; then
    echo "Please select a dev server"
    echo "Use -h or -help for help with $(basename "$0")"
    exit 1
fi

# Set the working directory
(cd /c/temp/logs/temp/ &&

    # Get the logs. Servers with multiple containers will have the following structure:
    #   HeaderA
    #   A
    #   A
    #   A
    #   HeaderB
    #   B
    #   B
    #   B
    now=$(date '+%Y%m%d_%H%M')
    ssh -tt "$user"@"$server" "sudo setfacl --modify user:${user}:rw /var/run/docker.sock && docker ps --format '{{.Names}}' | xargs -L 1 -t docker logs" > ./"${server}_${now}.log"

    # Process the temp file into individual files for each container ....
    # Get the headers for each Log File
    grep -n "docker logs" ./"${server}_${now}.log" >> ./docker_logs.txt
    total_matches=$(wc -l ./docker_logs.txt | cut -d' ' -f1)

    # From Line 1 -> First Match == Log A, From First Match -> Next Match == Log B, etc
    start_line=1

    # Get the file name for the first file
    file_name_match=$(head -n 1 ./docker_logs.txt)
    current_name=$(echo "$file_name_match" | cut -f2 -d: | sed "s/^docker logs //")

    # Get the end line index for the first file
    end_line_text=$(awk "NR==2" ./docker_logs.txt | cut -f1 -d:)
    if [[ $end_line_text ]]; then
        end_line=$(("$end_line_text"-1))
    else
        end_line="$"
    fi

    # Skipping the first file (starting from index 2), loop through any log files that are present
    for (( n=2; n<="$total_matches"+1; n++ )) do

        # Copy the current file from start -> end to the log file for the current name, if end_line was EOF
        # then break from the loop
        sed -n "${start_line},${end_line}p" ./"${server}_${now}.log" > ../"${server}_${now}_${current_name}.log"
        if [[ $end_line == "$" ]]; then
            break
        fi

        # Get the start line of the next file
        start_line=$(("$end_line"+1))

        # Get the file name of the next log file
        file_name_match=$(awk "NR==$n" ./docker_logs.txt)
        current_name=$(echo "$file_name_match" | cut -f2 -d: | sed "s/^docker logs //")

        # Get the ending index of the next log file, if there is nothing returned, set end_line to
        # be the EOF
        end_index=$(("$n"+1))
        end_line_text=$(awk "NR==$end_index" ./docker_logs.txt | cut -f1 -d:)
        if [[ $end_line_text ]]; then
            end_line=$(("$end_line_text"-1))
        else
            end_line="$"
        fi
    done

    # Remove the temp files
    rm -f /c/temp/logs/temp/*
)

# Open the logs directory for the user
start /c/temp/logs/

This produces N number of logfiles on the local system, of the format ${server}_${now}_${container_name}.log.

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2 Answers 2

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good

  • Good shbang line. (Consider env for PATH portability.)
  • Good variable names.
  • Good indentation.
  • Good comments

suggestions

  • I'm assuming you're replacing <SERVER_NAME> with some value in practice. If that is true, you might consider making that a variable so you can use this for other kinds of servers.
  • Using the subshell to let you change directories and get back to where you started is interesting, but unless you're getting some other non-obvious benefit from the subshell I'd use pushd /c/temp/logs/temp/ to get into the directory and popd to get out of it.
  • Double square brackets for shell conditionals have fewer surprises.
  • When doing shell math such as $(("$n"+1)) you don't need the quotes or the dollar sign. The double parens tell it to evaluate mathematically and that gets you variables too. So $((n+1)) will work just as well and is easier to read.
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  • \$\begingroup\$ I disagree on pushd and popd. They are much better suited for interactive use, and a nuisance in scripts. They also produce output that would need to be redirected away. \$\endgroup\$ Feb 23 at 10:47
  • \$\begingroup\$ They are also good for interactive use. Using a subshell still seems like the wrong choice. You could also store $PWD in another variable like $OLDPWD and cd back to that. \$\endgroup\$
    – chicks
    Feb 23 at 14:21
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Error messages should be redirected to stream 2 (standard error):

if [ "$foundServer" == 0 ]
then
    echo >&2 "Please select a dev server"
    echo >&2 "Use -h or -help for help with $(basename "$0")"
    exit 1
fi

Or,

if [ "$foundServer" == 0 ]
then
    exec >&2
    echo "Please select a dev server"
    echo "Use -h or -help for help with $(basename "$0")"
    exit 1
fi
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