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A Brief History of curl

curl was created in 1998 by Swedish developer Daniel Stenberg, who wrote its first version to automatically fetch currency exchange rates for an IRC bot in a Swedish chat channel — a small, personal itch, not a grand plan to build infrastructure. People kept asking for more protocols and more options, and the little utility grew into a general-purpose command-line tool for transferring data over HTTP, HTTPS, FTP, and eventually dozens of other protocols. Stenberg has remained curl's lead maintainer for essentially its entire life since; today curl ships by default on macOS, virtually every Linux distribution, and — since 2018 — Windows 10 and later, and it is estimated to run on billions of devices worldwide, from routers and cars to game consoles and nearly every continuous-integration pipeline that talks to an API. What began as a fix for one narrow personal problem is now arguably the single most widely deployed command-line HTTP client in existence, and one of the most quietly depended-upon pieces of open-source software on the internet.

Reading the Flags This Tool Generates

By default, curl does not follow HTTP redirects. If a server responds with a 301 or 302 status and a Location header pointing elsewhere, plain curl prints that redirect response — or an empty body — and stops; it does not automatically chase the new URL the way a web browser silently does. This trips up an enormous number of first-time curl users: a URL that works perfectly in a browser returns a confusing empty or wrong response from curl, for no apparent reason, simply because the browser followed a redirect curl didn't. The fix is the -L (--location) flag, which tells curl to follow the redirect chain to its final destination. It is such a common requirement that many engineers reach for -L by default any time they are not deliberately testing redirect behavior itself.

Once a command includes headers or body content containing spaces, quotes, or shell-special characters ($, &, ;, backticks), how you quote it stops being cosmetic — it is the difference between a request that works and one the shell mangles before curl ever sees it. A header like Authorization: Bearer abc 123 typed without quotes gets split by the shell at the space, so curl receives Authorization: and Bearer as two separate, broken arguments instead of one. Wrapping the whole value in single quotes tells the shell to treat everything inside literally, including spaces — but single quotes cannot contain a literal single-quote character themselves, since that character is what closes the quote. The standard escape for that case is to close the quote, insert a backslash-escaped single quote, and reopen the quote: '\''. This tool applies that escaping automatically to every value it inserts, so headers, body content, and auth credentials containing spaces, quotes, or other special characters always produce a command that runs correctly — without you needing to remember the escaping rules yourself.