Why the Church of England is taking on Shell

Dutch government promises support to Shell to cut CO2 emissions

tijdlijn

De UvA gaat voorlopig geen nieuwe onderzoekssamenwerkingen met Shell of soortgelijke bedrijven aan.

ClientEarth has today filed a world-first lawsuit against the Board of Directors of Shell plc for failing to manage the material and foreseeable risks posed to the company by climate change.

For sufficiently simple cases, just running a few commands sequentially, with no subshells, conditional logic, or loops, set -euo pipefail is sufficient (and make sure you use shellcheck -o all).

如何系统地学习Shell编程？

Bash maintains an internal hash of previously found executables in your path. In this case, it has details that at one time there was an executable at /usr/bin/siege, and reuses that path to avoid having to search again. You need to tell bash to manually rehash the path for siege like so: hash siege You can also clear all hashed locations: hash -r

Remember there are two kinds of variable. Internal Variables and Environment Variables. PATH should be an environment variable.

All shells should tell you that your path is the same thing with BOTH of the two commands: # The PATH variable echo "$PATH" # The PATH environment variable env | /bin/grep PATH

“These ads are intended to create a clean warm glow about the companies concerned, giving them more social licence to operate,” said Doug Parr, chief scientist for Greenpeace UK

$0 would be OK in most cases, some exceptions are, for instance, when the script you're executing is aliased (through alias in .bash_profile). You should really use $BASH_SOURCE variable, instead of $0.

Using $0 does not work when the script is run using source script or . script; the name of the script is not available.

Always use a while read construct: find . -name "*.txt" -print0 | while read -d $'\0' file do …code using "$file" done The loop will execute while the find command is executing. Plus, this command will work even if a file name is returned with whitespace in it. And, you won't overflow your command line buffer.

You can close the single quotes before starting the double quotes and do the reverse at the end of that inner section to achieve what you want:

mpv -playlist <(find "$PWD" -type f)

Just let it expand inside an array declaration's right side: list=(../smth*/) # grab the list echo "${#list[@]}" # print array length echo "${list[@]}" # print array elements for file in "${list[@]}"; do echo "$file"; done # loop over the array

The short answer is that you want an array: dirs=(/content/{dev01,dev01})

I think it's very confusing to overload common executables, such as yarn, in the /bin directory as I often put that bin directory first in my path. Thus, I'd unexpectedly get the bin/yarn rather than my system yarn, which I manage with yvm.

One good use for /dev/tty is if you're trying to call an editor in a pipeline (e.g., with xargs). Since the standard input of xargs is some list of files rather than your terminal, just doing, e.g., | xargs emacs will screw up your terminal. Instead you can use | xargs sh -c 'emacs "$@" </dev/tty' emacs to connect the editor to your terminal even though the input of xargs is coming from elsewhere.

Please make sure that your file(s) referenced in bin starts with #!/usr/bin/env node, otherwise the scripts are started without the node executable!

Since looping over the positional parameters is such a common thing to do in scripts, for arg defaults to for arg in "$@". The double-quoted "$@" is special magic that causes each parameter to be used as a single word (or a single loop iteration). It's what you should be using at least 99% of the time.

Bash (like all Bourne shells) has a special syntax for referring to the list of positional parameters one at a time, and $* isn't it. Neither is $@. Both of those expand to the list of words in your script's parameters, not to each parameter as a separate word.

Instead of using a for loop, which will fail on spaces unless you redefine the IFS variable, I would recommend using a while loop combined with find.

Different ways to prepend a line: (echo 'line to prepend';cat file)|sponge file sed -i '1iline to prepend' file # GNU sed -i '' $'1i\\\nline to prepend\n' file # BSD printf %s\\n 0a 'line to prepend' . w|ed -s file perl -pi -e 'print"line to prepend\n"if$.==1' file

for cpp_file in *.cpp; do gcc -c $$cpp_file & done; wait This gives much finer control than make -j.

There is one very important reason for enabling job control to be useful inside scripts: the side-effect it has of placing background processes in their own process groups. This makes it much, much easier to send signels to them and their children with one simple command: kill -<signal> -$pgid. All other ways of dealing with signaling entire trees of processes either involve elaborate (sometimes even recursive) functions, which are often bugnests, or risk killing the parent in the process (no pun intended).

To avoid the problems with different versions of echo you may want to use printf instead. In contrast to echo printf always interprets \ sequences but doesn't automatically add a linefeed at the end so you have to append \n at the end if you want one.

while (( "$#" )); do case "$1" in -a|--my-boolean-flag) MY_FLAG=0 shift ;; -b|--my-flag-with-argument) if [ -n "$2" ] && [ ${2:0:1} != "-" ]; then MY_FLAG_ARG=$2 shift 2 else echo "Error: Argument for $1 is missing" >&2 exit 1 fi ;; -*|--*=) # unsupported flags echo "Error: Unsupported flag $1" >&2 exit 1 ;; *) # preserve positional arguments PARAMS="$PARAMS $1" shift ;; esacdone# set positional arguments in their proper placeeval set -- "$PARAMS"

As a general rule: You should quote everything (that may be quoted).

For filter-branch, using pipelines like git ls-files | grep -v ... | xargs -r git rm might be a reasonable workaround but can get unwieldy and isn't as straightforward for users; plus those commands are often operating-system specific (can you spot the GNUism in the snippet I provided?)

However, the place where pip places that package might not be in your $PATH (thus requiring you to manually update your $PATH afterwards), and on windows the pip install might not take care of python-specific issues for you (see "Notes for Windows Users", above). As such, installation via package managers is recommended instead.

the bullet-proof way to add a path (e.g., ~/opt/bin) to the PATH environment variable is PATH="${PATH:+${PATH}:}~/opt/bin"

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.

source $stdenv/setup
genericBuild

$ ./my_script Will end up in STDOUT(terminal) and /var/log/messages $ tail -n1 /var/log/messages Sep 23 15:54:03 wks056 my_script_tag[11644]: Will end up in STDOUT(terminal) and /var/log/messages

exec &> >(tee -a "$log_file")

exec &> >(tee -a "$log_file") echo "This will be logged to the file and to the screen" $log_file will contain the output of the script and any subprocesses, and the output will also be printed to the screen.

Write stderr and stdout to a file, display stderr on screen (on stdout) exec 2> >(tee -a -i "$HOME/somefile.log") exec >> "$HOME/somefile.log" Useful for crons, so you can receive errors (and only errors) by mail

I just wanted to point out that the syntax is not supported by the POSIX standard and thus won't universally work in /bin/sh scripts (many people erroneously use bash syntax in /bin/sh scripts)

exec > >(tee "$HOME/somefile.log") 2>&1

#!/bin/sh # -*- tcl -*- # The next line is executed by /bin/sh, but not tcl \ exec tclsh "$0" ${1+"$@"}

When you have a pipeline, unbuffer must be applied to each element except the last (since that doesn't have its output redirected). Example: unbuffer p1 | unbuffer p2 | unbuffer p3 | p4

Operating systems implement a command-line interface in a shell for interactive access to operating system functions or services.

empty is an utility that provides an interface to execute and/or interact with processes under pseudo-terminal sessions (PTYs). This tool is definitely useful in programming of shell scripts designed to communicate with interactive programs like telnet, ssh, ftp, etc.

can be easily invoked directly from shell prompt or script

#!/bin/sh
empty -f -i in -o out telnet foo.bar.com
empty -w -i out -o in "ogin:" "luser\n"

#!/usr/bin/expect

spawn telnet foo.bar.com 
expect ogin {send luser\r}

does not use TCL, Perl, PHP, Python or anything else as an underlying language is written entirely in C has small and simple source code can easily be ported to almost all UNIX-like systems

The quirky looking printf is necessary to correctly expand the script's arguments in $@ while protecting possibly quoted parts of the command (see example below).

xargs -i sh -c 'test -f {} && echo {}'

If a program receives file names as arguments, don't join them with spaces. Use "$@" to access them one by one.

you can use "${@:1}" instead of shift, but that requires bash instead of sh in your #! shebang. IMHO your original shift approach is simpler and better

Given the deskopen script, you can use a reference to it as the shebang line in a .desktop file

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?)

non-interactive shells (actually when job control is not enabled)

In any case signal handling in shells is one of the least reliable and portable aspects. You'll find behaviours vary greatly between shells and often between different versions of a same shell. Be prepared for some serious hair pulling and head scratching if you're going to try to do anything non-trivial.

for sig in $(kill -l) ; do trap "echo parent:$sig" $sig done

read -rep $'\nDo you wish to stop playing?(y/n)' yn

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.

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.

if the process does not react on a normal kill, you may want to add an additional kill -9 a few seconds afterwards.

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

C.12. Release 1.6 (2013-09-10)In addition to the usual bug fixes, this release has several new features:The command nix-build --run-env has been renamed to nix-shell.

Never use x && y || z when y can return a non-zero exit status.

yell() { echo "$0: $*" >&2; } die() { yell "$*"; exit 111; } try() { "$@" || die "cannot $*"; }

If it's closing the "window" likely you're putting the exit # command inside a function, not a script. (In which case use return # instead.)

Bash (like all Bourne shells) has a special syntax for referring to the list of positional parameters one at a time, and $* isn't it. Neither is $@. Both of those expand to the list of words in your script's parameters, not to each parameter as a separate word.

However, this construct is not completely equivalent to if ... fi in the general case.

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.

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.

[[ -z "$a" || -z "$b" ]] && usage

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.

An even more general version that allows using find options:

readlink is not part of the standard. A portable script could be implemented with only POSIX shell features.

the following seems to do it without the bashism

Variables - Part 1

*

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

Philosophy

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:

Shell Scripting Tutorial

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}

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.

{ read foo ; read filesystem size using avail prct mountpoint ; } < <(df -k /)

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.

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.

Apple replaced Bourne Again SHell with Z shell for licensing reasons

And I continue to tell people: Friends don't let friends write bash script.

# 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

ps f

\curl

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.

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.