4/10/2024 0 Comments What does quote mean in terminal2.1 Why do we need a shell quoting mechanism? Index The characters are passed, unchanged, to the command. Quoting hides the special character(s) from processing by the shell. $ echo 'Semicolon is special quoting hides it from the shell.' Semicolon is special quoting hides it from the shell. $ echo Semicolon is special\ quoting hides it from the shell. “Quoting” is the generic name given to the action of protecting shell meta-characters from being treated specially by the shell, usually by surrounding the string containing the special character(s) with quotes, or using backslashes in front of the individual characters: $ echo Semicolon is special it divides command lines. Other shell meta-characters include: $, *,, >, ?, &, |, etc. The shell separates arguments with one blank or a dozen blanks. The most common shell meta-character is the blank or space character that shells use to separate arguments. Shells treat a number of characters specially on the command lines these are called shell “meta-characters”. Shells read input and find and run commands, passing command line arguments to the commands. 2 Quoting – hiding characters from the shell Index “Sanitizing inputs” refers to the process of removing special characters from the input so that they don’t defeat the quoting used in the query and change the meaning of the query. The SQL query now tries to find a student named 'Robert' and then (after the semicolon ) deletes the entire Students table from the database. Leslie Smith, the query simply looks up the student by name in the database: SELECT * FROM Students WHERE ( NAME = 'Leslie Smith' ) įor little Bobby Tables, his name Robert') DROP TABLE Students also gets inserted into the database query in place of $NAME in the same way, but the presence of quotes and other special characters in the name completely changes the meaning of the query: SELECT * FROM Students WHERE ( NAME = 'Robert') DROP TABLE Students ' ) For a normal student name used in place of $NAME, e.g. The variable $NAME is the name of the student, and the query would be modified by inserting that name into the query in place of the $NAME variable. A database query in SQL might look like this: SELECT * FROM Students WHERE ( NAME = '$NAME' ) Only the characters being quoted are passed to the command.Īnother Quote Tutorial: 1.1 The Bobby Tables Problem Index The Bobby Tables Problem – īelow and in the next link are explanations of what happened in the above comic.ĭatabases are accessed using a query language, typically Structured Query Language. The quoting delimits (identifies) a string of characters the quoting mechanism is removed and is not part of the string passed to the command. Single quotes, double quotes, and backslashes tell the shell which parts of command lines to treat as ordinary (not special) characters. 14 ADVANCED SHELL: eval: Using quotes inside shell variables.13 ADVANCED SHELL: Quoting for remote shells ( ssh).12 Using argv.sh to count command line arguments.11 Studies in Quoting Special Characters.10 Quotes inside variables are not special.7.2.4 Always double-quote variable expansions.7.2.3 Quoting text containing variables.7.2.2 Quoting text containing both single and double quotes.7.2.1 Quotes inside quotes are not meta-characters.7.2 How to quote text containing other quotes?.7 When to use single quotes, double quotes, backslashes.6 Shell Quote Processing is Left to Right.5 Quoting is removed from the argument being quoted.4 Three quoting mechanisms: double, single, backslash.3.1 Quoting used by other programs such as grep and find.3 Which programs have quoting mechanisms?.
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