85 Matching Annotations
  1. Last 7 days
    1. Now this probably won't make difference in the real world (e.g. because the exit codes are not portable and on top of that not always unambiguous as discussed in Default exit code when process is terminated?)
    1. read -rep $'\nDo you wish to stop playing?(y/n)' yn
    2. You also need job controlled -monitoring in your parent so it keep track of its children. wait, for example, only works at all with job control. -monitor mode is how shells interact with terminals.
    1. The parentheses always start a subshell. What's happening is that bash detects that sleep 5 is the last command executed by that subshell, so it calls exec instead of fork+exec. The sleep command replaces the subshell in the same process.
    1. The command nix-shell will build the dependencies of the specified derivation, but not the derivation itself. It will then start an interactive shell in which all environment variables defined by the derivation path have been set to their corresponding values, and the script $stdenv/setup has been sourced. This is useful for reproducing the environment of a derivation for development.

      QUESTION: What exactly does nix-shell execute from the Nix expression (i.e., shell.nix, default.nix, etc.)?

      ANSWER: Based on my current understanding, the answer is everything. It calls $stdenv/setup (see annotation below) to set up the most basic environment variables (TODO: expand on this), and "injects" the most common tools (e.g., gcc, sed) into it.

      It also defines the phases (TODO: verify this) and builder functions, such as genericBuilder. For example, the default builder is just two lines:

      source $stdenv/setup
      genericBuild
      

      TODO: pkgs/stdenv/generic/builder.sh is a mystery though.

      QUESTION: Once dropping into nix-shell, how do I know what phases to execute by looking at a default.nix? (E.g., [..]freeswitch/default.nix)

      ANSWER: As far as I can tell, one can override the phases in their Nix build expression (to build the derivation, see at the bottom), but they won't get executed as only the $stdenv/setup (see above) will get sourced, and no builders are called that, in return, invoke the phases (again, see above).

      So if one is using nix-shell

      • to create/hack on a package, the person has to manually invoke the builder or phases (TODO: still fuzzy on this subject)

      • to set up an environment, then one doesn't even have to worry about builders/phases because we just use nix-shell to clear the environment and to inject tools that we need for a given task

      QUESTION: When dropping into nix-shell, is this Nix expression (i.e., freeswitch/default.nix) executed? Or just parts of it?

      ANSWER: As stated above, all of the input Nix expression is evaluated, but no builders and build phases are called; although, nothing prevents one to override the phases, in case they are creating/hacking on a package.

      QUESTION:

      The command nix-shell will build the dependencies of the specified derivation, but not the derivation itself.

      What is the "derivation" here exactly? I know that it is a build expression, but does that mean the default.nix (or other Nix expression) nix-shell is invoked with?

      <sup>This statement also seems like a contradiction with how `nix-shell` works (i.e., if one issues `nix-shell -p curl`, then `curl` will be available in that sub-shell), but `-p` acts like a shortcut to as if `curl` had been listed in `buildInputs` so this is not the case.</sup>

      ANSWER: I have the feeling my confusion comes from the fact that the term "derivation" is used ambiguously in the manuals, sometimes to mean multiple things (see list below).

      TODO: Substantiate this claim, and make sure that it not coming from my misunderstanding certain topics.

      • Nix build expression (such as default.nix) whose output is going to become the store derivation itself (see last item at the bottom about the Nix manual's glossary definition)

      • store derivation.

      Had multiple cracks at unambiguously define what a derivation is, and here's a list of these:

  2. Feb 2021
    1. example: get an environment which is used to build irssi (also see nix-shell) $ nix-build $NIXPKGS --run-env -A irssi example: get a persistent environment which is used to build irssi $ nix-build $NIXPKGS --run-env -A irssi --add-root

      nix-build <path> --run-env has been superseded by nix-shell. From Nix manual section C.12. Release 1.6 (2013-09-10):

      The command nix-build --run-env has been renamed to nix-shell.

  3. Nov 2020
    1. The potential problem: if second_task fails, third_task will not run, and execution will continue to the next line of code - next_task, in this example. This may be exactly the behavior you want. Alternatively, you may be intending that if second_task fails, the script should immediately exit with its error code. In this case, the best choice is to use a block - i.e., curly braces: first_task && { second_task third_task } next_task Because we are using the -e option, if second_task fails, the script immediately exits.
    2. When people write COND && COMMAND, typically they mean "if COND succeeds (or is boolean true), then execute COMMAND. Regardless, proceed to the next line of the script." It's a very convenient shorthand for a full "if/then/fi" clause.
    1. zip -r myfile.zip ./filename

      把filename 压缩成 myfile.zip

      unzip -d /home/file myfile.zip

      把myfile.zip 压缩到 home/file 目录下

      zip -d myfile.zip smart.txt

      删除 myfile.zip 中的 smart.txt

      zip -m myfile.zip add.txt

      往 myfile.zip 中加 add.txt

    1. It starts truncating it's output (shortening strings with ...) once you pipe it's output into grep. That is quite unacceptable. When I am checking if something is inhibited in a script, I should have all possible information available and not have to consider if a string will get truncated when being piped into a tool, that is perfectly readable on a wide terminal.
  4. Oct 2020
    1. *

      * 应该表示当前文件夹内的文件, 类似于 ls

    2. begins with a special symbol: #. This marks the line as a comment

      以#开头的代码表示这行代码被注释掉了,这点跟 Python 一致。

    1. Note that to make a file executable, you must set the eXecutable bit, and for a shell script, the Readable bit must also be set:

      这句话没懂

    2. Shell Scripting Tutorial

      shell 编程教程

  5. Aug 2020
    1. You can also nest brace expansion lists in the mkdir command. For example, in the articles subdirectory under the htg directory, we want to create two subdirectories called new and rewritten. So, we type the following command at the prompt and press Enter. mkdir -p htg/{articles/{new,rewrites},images,notes,done}
  6. Jul 2020
    1. The most commonly supported tool for this is kerl. Kerl is a wrapper around downloading, compiling, and loading various Erlang/OTP versions on a single system, and will abstract away most annoying operations.
  7. Jun 2020
  8. May 2020
    1. I have used this bash one-liner before set -- "${@:1:$(($#-1))}" It sets the argument list to the current argument list, less the last argument.

      Analogue of shift built-in. Too bad there isn't just a pop built-in.

  9. Apr 2020
    1. Invert the exit code of a process. Make 0 into 1 and everything else into a 0. An alternative to ! some-command syntax present in some shells.
    1. # Add auto-completion and a stored history file of commands to your Python # interactive interpreter. Requires Python 2.0+, readline. Autocomplete is # bound to the Esc key by default (you can change it - see readline docs). # # Store the file in ~/.pystartup, and set an environment variable to point # to it: "export PYTHONSTARTUP=~/.pystartup" in bash. import atexit import os import readline import rlcompleter historyPath = os.path.expanduser("~/.pyhistory") def save_history(historyPath=historyPath): import readline readline.write_history_file(historyPath) if os.path.exists(historyPath): readline.read_history_file(historyPath) atexit.register(save_history) del os, atexit, readline, rlcompleter, save_history, historyPath

      Enable history and sane keys in python shell

  10. Feb 2020
  11. Jan 2020
    1. ps f

      this doesn't run on my system. However ps -f seems to list processes started in the terminal and ps -ef lists all (?) processes

  12. Dec 2019
    1. Point to be noted is, there is a backslash before curl. This prevents misbehaving if you have aliased it with configuration in your ~/.curlrc file.
    1. As for exec, I am just using it because it makes sense to run the final command in the same process, replacing the wrapper script instead of spawning a new process. It's not strictly necessary.
    1. For those (like me) wondering why is the space needed, man bash has this to say about it: > Note that a negative offset must be separated from the colon by at least one space to avoid being confused with the :- expansion.
    1. Do not start ssh-agent from .bashrc or .zshrc, since these files are executed by each new interactive shell. The place to start ssh-agent is in a session startup file such as .profile or .xsession.
  13. Nov 2019
  14. Sep 2019
  15. Jul 2019
    1. 将错误IP放到数组里面判断是否ping失败三次
      #!/bin/bash  
      IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"
      for IP in $IP_LIST; do
          NUM=1
          while [ $NUM -le 3 ]; do
              if ping -c 1 $IP > /dev/null; then
                  echo "$IP Ping is successful."
                  break
              else
                  # echo "$IP Ping is failure $NUM"
                  FAIL_COUNT[$NUM]=$IP
                  let NUM++
              fi
          done
          if [ ${#FAIL_COUNT[*]} -eq 3 ];then
              echo "${FAIL_COUNT[1]} Ping is failure!"
              unset FAIL_COUNT[*]
          fi
      done
      
    2. 获取随机8位字符串:
      方法1:
      # echo $RANDOM |md5sum |cut -c 1-8
      471b94f2
      方法2:
      # openssl rand -base64 4
      vg3BEg==
      方法3:
      # cat /proc/sys/kernel/random/uuid |cut -c 1-8
      ed9e032c
      
    3. 获取随机8位数字:

      方法1:

      # echo $RANDOM |cksum |cut -c 1-8
      23648321
      方法2:
      # openssl rand -base64 4 |cksum |cut -c 1-8
      38571131
      方法3:
      # date +%N |cut -c 1-8
      69024815
      
    4. 注意事项

      1)开头加解释器:#!/bin/bash

      2)语法缩进,使用四个空格;多加注释说明。

      3)命名建议规则:变量名大写、局部变量小写,函数名小写,名字体现出实际作用。

      4)默认变量是全局的,在函数中变量local指定为局部变量,避免污染其他作用域。

      5)有两个命令能帮助我调试脚本:set -e 遇到执行非0时退出脚本,set-x 打印执行过程。

      6)写脚本一定先测试再到生产上。

  16. Dec 2018
  17. Oct 2018
  18. Jun 2018
  19. Dec 2017
    1. #!/bin/sh(cat <<EOFstart(){    echo "start"}EOF) >/tmp/b

      shell 如何把多行内容输出到一个文件

  20. Oct 2017
  21. Feb 2017
    1. A shell script is a file of executable commands that has been stored in a text file. When the file is run, each command is executed.

      The power of BASH!

  22. Aug 2015
  23. May 2015
    1. You can push an alternative branch to Heroku using Git. git push heroku-dev test:master This pushes your local test branch to the remote's master branch (on Heroku).

      Push a local non-master branch to heroku master

    1. Every shell has some startup files that it consults for its configuration. Zsh has system-wide startup items in /etc/ (or, in distributions such as Ubuntu, in /etc/zsh/) and user-specific startup files (in the home directory). When Zsh starts up, it reads the following things in this order: /etc/zshenv and ~/.zshenv If the shell is a login shell: /etc/zprofile and ~/.zprofile If it’s an interactive shell: /etc/zshrc and ~/.zshrc If the shell is a login shell: /etc/zlogin and ~/.zlogin And when a user logs out from a login shell, Zsh reads /etc/zlogout and ~/.zlogout. To work out which commands you have to write in which startup files, it's important to know the different types of shells. A login shell is one that's spawned when you log in - for example, via SSH or on a virtual terminal. An interactive shell displays a prompt to the user where you can type commands - for instance, when you open a terminal window in Ubuntu. However, if you run ssh host somecommand, then this is a login shell, but is in fact a non-interactive one.
    2. Every shell has some startup files that it consults for its configuration. Zsh has system-wide startup items in /etc/ (or, in distributions such as Ubuntu, in /etc/zsh/) and user-specific startup files (in the home directory). When Zsh starts up, it reads the following things in this order: /etc/zshenv and ~/.zshenv If the shell is a login shell: /etc/zprofile and ~/.zprofile If it’s an interactive shell: /etc/zshrc and ~/.zshrc If the shell is a login shell: /etc/zlogin and ~/.zlogin And when a user logs out from a login shell, Zsh reads /etc/zlogout and ~/.zlogout. To work out which commands you have to write in which startup files, it's important to know the different types of shells. A login shell is one that's spawned when you log in - for example, via SSH or on a virtual terminal. An interactive shell displays a prompt to the user where you can type commands - for instance, when you open a terminal window in Ubuntu. However, if you run ssh host somecommand, then this is a login shell, but is in fact a non-interactive one.
    3. There's also a function periodic() that is executed every PERIOD seconds if the latter variable is set.

      Periodic commands in ZSH

    4. Zsh also makes it possible to run particular code automatically on certain occasions. You just have to define some special functions. The two most frequently used are chpwd and precmd. Zsh calls the former each time the current directory changes. The latter is called just before Zsh shows you a new prompt. Both functions are regularly used to show the current directory in the title bar of your terminal emulator. If you use programs other than the shell, which alter the title of your terminal emulator (Vim is one example), you should use precmd - it restores the title after another command has run. So this is how we show the current directory in the title bar (adapted from the manual page):

      Run commands

    5. REPORTTIME=5 TIMEFMT="%U user %S system %P cpu %*Es total"

      Report times of long running shell commands