{"id":243,"date":"2026-10-13T02:02:13","date_gmt":"2026-10-13T02:02:13","guid":{"rendered":"http:\/\/www.scmgalaxy.com\/tutorials\/2010\/04\/16\/interview-questions-sets-shell-script-descriptive\/"},"modified":"2026-10-13T02:02:13","modified_gmt":"2026-10-13T02:02:13","slug":"interview-questions-sets-shell-script-descriptive","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/interview-questions-sets-shell-script-descriptive\/","title":{"rendered":"Shell Scripting Interview Questions, Explained: Bash Fundamentals, UNIX Processes, and Practical Commands"},"content":{"rendered":"\n

This revised guide turns the original long Q&A into a practical reference for engineers preparing for Bash and UNIX interviews. It focuses on topics that show up in real DevOps work: scripting, command execution, redirection, permissions, and process control. Original post: Shell Bash Scripting Interview Questions and Answer \u2013 Part 1<\/a>.<\/p>\n\n\n\n

Originally published on 2010-04-16; fully revised and updated.<\/em><\/p>\n\n\n\n

\"shell-script-descriptive-interview-questions-sets\"<\/figure>\n\n\n\n

What shell scripting is and why it matters<\/h2>\n\n\n\n

Shell scripting means writing command-line instructions in a text file and running them through a shell interpreter such as bash<\/code>, sh<\/code>, or ksh<\/code>. It is primarily used for automation on UNIX-like systems, and it often acts as glue between OS tools, CI jobs, and deployment scripts.<\/p>\n\n\n\n

  • Automates repetitive admin tasks.<\/li>
  • Combines existing tools quickly without compiling code.<\/li>
  • Works well for bootstrapping, CI\/CD steps, and operational runbooks.<\/li>
  • Can be risky when scripts are unquoted or run with destructive commands.<\/li><\/ul>\n\n\n\n

    How a shell command executes under the hood<\/h2>\n\n\n\n

    Many interview questions around fork<\/code>, exec<\/code>, return codes, and zombies become easier once you understand the command lifecycle.<\/p>\n\n\n\n

    \nflowchart TD\n    A[User enters command] --> B[Shell parses tokens and expansions]\n    B --> C{Builtin}\n    C -- yes --> D[Run builtin in current shell]\n    C -- no --> E[Fork child process]\n    E --> F[Exec program in child]\n    F --> G[Program exits with status]\n    D --> H[Shell records exit code]\n    G --> H\n    H --> I[Prompt returns]\n<\/pre>\n\n\n\n
    If the command is an external program, the shell usually creates a child process and then executes that program in the child. The exit code is returned to the shell, which makes it available as $?<\/code>.<\/p>\n\n\n\n
    Essential interview topics with practical command examples<\/h2>\n\n\n\n
    Exit codes and command chaining<\/h3>\n\n\n\n
    By convention, exit code 0<\/code> means success and non-zero means failure. Operators like &&<\/code> and ||<\/code> chain commands based on that status.<\/p>\n\n\n
    #!\/usr\/bin\/env bash<\/span>\ngrep -q \"ready\"<\/span> app.log\necho<\/span> \"Last exit code: $?\"<\/span>\n\ngrep -q \"ready\"<\/span> app.log && echo<\/span> \"Service is ready\"<\/span> || echo<\/span> \"Service is not ready\"<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    Stdin, stdout, and stderr (file descriptors 0, 1, 2)<\/h3>\n\n\n\n
    Standard input, output, and error are core to shell pipelines and logging strategy.<\/p>\n\n\n
    my_command<\/span> >stdout<\/span>.log<\/span> 2>stderr<\/span>.log<\/span>\nmy_command<\/span> >combined<\/span>.log<\/span> 2>&1\nmy_command<\/span> <input<\/span>.txt<\/span><\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\n
    Executing a script vs sourcing a script<\/h3>\n\n\n\n
    Method<\/th>Typical syntax<\/th>Runs in current shell<\/th>Can change current shell environment<\/th><\/tr><\/thead>
    Execute script<\/td>.\/script.sh<\/code><\/td>No<\/td>No<\/td><\/tr>
    Source script<\/td>source .\/script.sh<\/code> or . .\/script.sh<\/code><\/td>Yes<\/td>Yes<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n
    # env-demo.sh<\/span>\nexport DEMO_VALUE=\"set-by-script\"<\/span>\n\n.\/env-demo.sh\necho<\/span> \"$DEMO_VALUE\"<\/span>    # usually empty in parent shell<\/span>\n\nsource .\/env-demo.sh\necho<\/span> \"$DEMO_VALUE\"<\/span>    # now visible in current shell<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    Shebang and interpreter selection<\/h3>\n\n\n\n
    The shebang is the first line of an executable script and selects the interpreter.<\/p>\n\n\n
    #!\/usr\/bin\/env bash<\/span>\nset -euo pipefail\necho<\/span> \"Running with Bash $BASH_VERSION\"<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    Permissions, links, and file access fundamentals<\/h2>\n\n\n\n
    Interviewers frequently ask how to set permissions and how links behave in UNIX filesystems.<\/p>\n\n\n
    chmod<\/span> 664 myfile<\/span>\nchmod<\/span> u<\/span>+rwx<\/span>,g<\/span>+rx<\/span>,o-rwx<\/span> deploy<\/span>.sh<\/span>\nls<\/span> -l<\/span> deploy<\/span>.sh<\/span><\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\n
    Link type<\/th>What it references<\/th>Cross-filesystem support<\/th>Typical command<\/th><\/tr><\/thead>
    Hard link<\/td>Same inode as target file<\/td>No<\/td>ln file1 file2<\/code><\/td><\/tr>
    Symbolic link<\/td>Path to another file or directory<\/td>Yes<\/td>ln -s file1 link1<\/code><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    Command comparisons often asked in interviews<\/h2>\n\n\n\n
    Command<\/th>Comparison style<\/th>Best for<\/th>Example<\/th><\/tr><\/thead>
    cmp<\/code><\/td>Byte-by-byte; reports first mismatch<\/td>Quick binary or exact byte comparison<\/td>cmp fileA fileB<\/code><\/td><\/tr>
    diff<\/code><\/td>Line-by-line differences<\/td>Text review and patch-style output<\/td>diff -u fileA fileB<\/code><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    Process management, signals, daemons, and IPC<\/h2>\n\n\n\n
    Core process questions usually center on process IDs, states, and signaling. A daemon is a background service process detached from an interactive terminal session.<\/p>\n\n\n
    sleep 300<\/span> &\nBG_PID=$!\n\nps -p \"$BG_PID\"<\/span> -o pid,ppid,stat,cmd\nkill \"$BG_PID\"<\/span>      # graceful request<\/span>\nkill -9<\/span> \"$BG_PID\"<\/span>   # force kill if needed<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    Common inter-process communication (IPC) mechanisms include unnamed pipes, named pipes (FIFO), sockets, message queues, and shared memory.<\/p>\n\n\n
    mkfifo \/tmp\/demo.fifo\n\n# terminal 1<\/span>\ncat \/tmp\/demo.fifo\n\n# terminal 2<\/span>\necho<\/span> \"hello via fifo\"<\/span> > \/tmp\/demo.fifo<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    Login shells, non-login shells, and environment variables<\/h2>\n\n\n\n
    Startup files differ by shell implementation. The table below reflects common Bash behavior on Linux and UNIX-like systems.<\/p>\n\n\n\n
    Session type<\/th>Common Bash startup files<\/th>Typical use<\/th><\/tr><\/thead>
    Login shell<\/td>\/etc\/profile<\/code>, then one of ~\/.bash_profile<\/code>, ~\/.bash_login<\/code>, or ~\/.profile<\/code><\/td>User environment initialization<\/td><\/tr>
    Interactive non-login shell<\/td>~\/.bashrc<\/code><\/td>Aliases, prompt, interactive shell options<\/td><\/tr>
    Non-interactive shell<\/td>May use BASH_ENV<\/code> if set<\/td>Script-time environment setup<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n
    echo<\/span> \"Login shell from env: $SHELL\"<\/span>\nps -p $$ -o comm=\nshopt -q login_shell && echo<\/span> \"login shell\"<\/span> || echo<\/span> \"non-login shell\"<\/span>\n\nexport APP_ENV=prod\necho<\/span> \"$APP_ENV\"<\/span>\nunset<\/span> APP_ENV<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    Rapid-fire interview questions and concise answers<\/h2>\n\n\n\n
    • What does $?<\/code> store?<\/strong> The exit status of the most recently executed command.<\/li>
    • What are file descriptors 0, 1, and 2?<\/strong> Standard input, standard output, and standard error.<\/li>
    • Difference between \"$*\"<\/code> and \"$@\"<\/code>?<\/strong> \"$*\"<\/code> joins all positional parameters into one word; \"$@\"<\/code> preserves each parameter as a separate word.<\/li>
    • What is IFS<\/code>?<\/strong> The internal field separator used during word splitting.<\/li>
    • What is a zombie process?<\/strong> A terminated child process whose parent has not yet collected its exit status with wait<\/code>.<\/li>
    • What does exec<\/code> do in shell?<\/strong> Replaces the current shell process with the specified program.<\/li>
    • How do you make a script executable?<\/strong> Add execute permission, for example chmod +x script.sh<\/code>.<\/li><\/ul>\n\n\n\n
      Best practices and common pitfalls<\/h2>\n\n\n\n
      • Quote variable expansions (for example \"$var\"<\/code>) to avoid word-splitting bugs.<\/li>
      • Check exit codes and fail fast for automation workflows.<\/li>
      • Use set -euo pipefail<\/code> in Bash scripts where appropriate.<\/li>
      • Be careful with destructive commands like rm<\/code>, redirection, and wildcards.<\/li>
      • Prefer explicit paths in cron\/CI contexts where environment variables differ.<\/li>
      • Lint scripts with tools such as shellcheck<\/code> before production use.<\/li><\/ul>\n\n\n\n
        A strong interview answer is not just a definition; it shows that you understand safe operational behavior, process control, and debugging in real shell automation.<\/p>\n","protected":false},"excerpt":{"rendered":"
        A modernized, interview-focused guide to shell scripting and core UNIX concepts for DevOps engineers. Learn command execution flow, redirection, permissions, process control, IPC, and safe scripting patterns with practical examples.<\/p>\n","protected":false},"author":1,"featured_media":4303,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_joinchat":[],"footnotes":""},"categories":[52],"tags":[641,3969,766,3968,3961,507,1553,482,1830,3910,138,3046,3960,3970,3966,3965,3964,3963,3967,3962,637],"class_list":["post-243","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-interview-questions-answers","tag-answers","tag-descriptive-shell-script-interview-question-and-answers","tag-interview","tag-interview-questions-answer-for-shell-script","tag-interview-questions-sets","tag-list","tag-most-asked","tag-questions","tag-selected","tag-sets","tag-shell","tag-shell-script","tag-shell-script-descriptive","tag-shell-script-descriptive-interview-question-and-answers","tag-shell-script-interview-guide","tag-shell-script-interview-qa","tag-shell-script-interview-questions-answers","tag-shell-script-job-interview","tag-shell-script-job-interview-kit","tag-shell-scripting-interview","tag-top"],"_links":{"self":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/243","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/comments?post=243"}],"version-history":[{"count":4,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/243\/revisions"}],"predecessor-version":[{"id":79073,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/243\/revisions\/79073"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/media\/4303"}],"wp:attachment":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/media?parent=243"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/categories?post=243"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/tags?post=243"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}