What do they do? Are there more of them? Meta thread about this question. Improve this question. Add a comment. Active Oldest Votes. A newline after command1 is optional. This command can also be written if command1 then command2 else false fi or simply if command1; then command2; fi if the return status is ignored. This command can also be written if command1 then true else command2 fi or in a shorter way if! If the right side of this redirection is a file please read the next entry.
It is often used to print multi-line strings. Improve this answer. It would probably be worthwhile noting that not all shells are equal, and specifically highlighting the bash-specific features.
GregHewgill yeah, I weaseled out of it by saying that I am discussing with respect to bash. I'm hoping someone else will pitch in and answer for non bash shells, but highlighting the bash-specific ones makes a lot of sense. I'll have to check though, I don't know which they are off the top of my head. This answer also discusses very little about how they work - for example, it is almost worse than useless to talk about a simple command and a command without explaining what these are and how the shell decides.
They work on bash and zsh though. I don't know what, if anything, is truly bash-specific in that list. I should go through this and add the shells each works in but that would involve finding out first.
Arc No, they don't evaluate to true or false, that's a completely different context. This just means that an exit value of non-0 indicates a problem not false and an exit code of 0 indicates success not true. That's always been the way and is quite standard.
A non-0 exit code indicates an error in every environment I know of. Show 10 more comments. And remember also Redirection of output causes the file … to be opened for writing ….
So, what to do about it? You may need to use an option like -a or -p on cp to tell it to preserve attributes. These answers have the advantage that they do not require any free space or they require very little. Exception: sort … dd … will probably require lots of free space, because sort needs to read all of its input before it can write any output, and it probably buffers most if not all of that data in a temporary file. Note: Some programs e.
See this answer for a discussion of the above, and a script that makes this answer work if your command is guaranteed to produce the same amount of output data as there is input or less.
So, what was the question? How can I make iconv replace the input file with the converted output? Can I read and write to the same file in Linux without overwriting it? Redirect to the same file as the source file processed by the command Why does this sort command give me an empty file?
Redirecting tr stdout to a file grep: input file 'X' is also the output Do redirection operators open file descriptors in parallel? I have no affiliation with the blog that I cited, above. Scott Scott 9, 8 8 gold badges 37 37 silver badges 63 63 bronze badges.
Should I post it here and maybe link to it from some of the other more heavily trafficked questions , or should I move it to one of the questions that actually raises this issue? Also, is this perhaps a situation where questions should be merged? Applications shall be allowed to create files in this directory, but shall not assume that such files are preserved between invocations of the application.
See this or this for demos on here-document handling. Also why the same amount of output or less warning? And, if the output is larger than the input e. Show 6 more comments. For example, you can say command1 ; with no command2. This is equivalent to command1 i. Then, regardless of the result of running that first command, run command2 and wait for it to finish.
Then, if command2 succeeded, Run command3 and wait for it to finish. Then, regardless of the result of running that command, run command4 and wait for it to finish. If command2 failed, stop processing the command line. I said they were not relevant because I did not want to go into that much detail. I wanted an answer that could work as a quick cheatsheet for newbies who're wondering what all the weird squiggles at the end of the various commands are. All of the lines read up to that point are then used as the standard input or file descriptor n if n is specified for a command.
No parameter and variable expansion, command substitution, arithmetic expansion, or filename expansion is performed on word. If any part of word is quoted, the delimiter is the result of quote removal on word , and the lines in the here-document are not expanded. This allows here-documents within shell scripts to be indented in a natural fashion. The word undergoes tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote removal.
Filename expansion and word splitting are not performed. The result is supplied as a single string, with a newline appended, to the command on its standard input or file descriptor n if n is specified. If word expands to one or more digits, the file descriptor denoted by n is made to be a copy of that file descriptor.
If the digits in word do not specify a file descriptor open for input, a redirection error occurs. If n is not specified, the standard input file descriptor 0 is used. If n is not specified, the standard output file descriptor 1 is used. Develop and improve products. List of Partners vendors. Tim Fisher. VP and General Manager, Lifewire.
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